This is a public working draft of XML Schema 1.0 for review by the
public and by members of the World Wide Web Consortium.
Following a period of review and polishing, it is the WG's intent
to issue a Last Call for Review by other W3C working groups sometime
during March, 2000, and to submit this specification thereafter for publication as a Candidate Recommendation. This schedule
may vary, depending on the comments of the public and of other W3C
working groups on this draft. Such comments are instrumental in the
WG's deliberations, and we encourage readers to review the draft and send comments to
www-xml-schema-comments@w3.org
This working draft has been substantially restructured since the previous public
release. This structural reorganisation is not yet complete.
In this
draft, unrestructured material is distinguished as follows:
The restructuring of Chapters 1 through 3 is largely completed:
Attributes and Attribute groups give the clearest picture of how Chapters 5 and
6 will eventually look.
The lengthy introductory example material from the old Chapter 2 has
been moved out of line into a non-normative companion document ([XML Schema: Exposition] and expanded
considerably. Pointers to this will in due course be added to this document.
Although the Working Group does not anticipate further substantial
changes to the functionality described here, this is still a working
draft, subject to change. The present version should
be implemented only by those interested in providing a check on
its design or by those preparing for an implementation of the
Candidate Recommendation. The Schema WG will
not allow early implementation to constrain its ability to make changes to this
specification prior to final release.
1 Introduction
This document sets out the structural part (XML Schema: Structures) of the XML Schema definition language.
Chapter 2 presents a Conceptual Framework (§2) for XML Schemas, including
an introduction to the nature of XML Schemas and a formal specification
of the XML Schema abstract data model, along with
other terminology used throughout this document.
Chapter 3, Schema Component Details (§3), specifies the precise
semantics of each component of the abstract model.
Chapter 4, XML Representation of Schemas and Schema Components (§4), presents the XML representation
that maps to the abstract model, in the form
of a DTD and XML Schema for an XML Schema document type, along with rules and
conventions for identifying the components needed for any particular
validation.
Chapter 5 presents Schema Access and Composition (§5), including the
connection between documents and schemas, the import and inclusion of declarations and definitions and
the foundations of schema-validity.
Chapter 6 discusses Conformance * (§6), including the rules
by which documents are validated, and responsibilities of schema-aware
processors.
The normative appendices include a (normative) DTD for Schemas (§B)
and a (normative) Schema for Schemas (§A) for the transfer syntax, a Glossary (normative) * (§C) [not yet written] and
References (normative) * (§D).
1.1 Purpose
The purpose of XML Schema: Structures is to define the nature of XML schemas
and their component parts,
provide an inventory of XML markup
constructs with which to represent schemas, and define the
application of schemas to XML documents.
The purpose of an XML Schema: Structures schema is to define and describe a class of
XML documents by using schema components to constrain and document the meaning,
usage and relationships of their constituent parts: datatypes, elements and
their content and attributes and their values. Schemas may also provide for the specification of additional
document information, such as default values for attributes
and elements. Schemas have
facilities for self-documentation. Thus, XML Schema: Structures can be used to define, describe and catalogue XML
vocabularies for classes of XML documents.
Any application that consumes well-formed XML can use the XML Schema: Structures
formalism to express syntactic, structural and value constraints applicable to
its document instances. The XML Schema: Structures formalism allows a useful level of
constraint checking to be described and validated for a wide spectrum of XML
applications. However, the language defined by this specification does not attempt to provide
all the facilities that might be needed by any
application. Some applications may require constraint capabilities not
expressible in this language, and so may need to perform their own additional
validations.
1.3 Documentation Conventions and Terminology
The following highlighting and typography is used to present technical material in
this document:
Special terms are defined at their point of
introduction in the text; hyperlinks connect other uses of the
term to the definition. For example, a definition of
term might read: [Definition:] A term is
something we use a lot. The definition is labeled as such and the term is highlighted
typographically. The end of the definition is not specially marked
in the displayed or printed text.
The following terms are used in building
definitions and describing the actions of XML Schema: Structures processors:
-
[Definition:] may
-
Conforming documents and processors are permitted to but need
not behave as described.
[Unrestructured material elided]
Non-normative examples are set off
typographically and accompanied by a brief
explanation:
| Example |
<schema
targetNamespace="http://www.muzmo.com/XMLSchema/1.0/mySchema" >
|
|
| And an explanation of the example. |
|
The definition of each kind of schema component consists of a list of
its properties and their contents, followed by descriptions of the
semantics of the properties:
The correspondence between an element information item which is part
of the XML representation of a schema and one or more schema components is presented in a tableau
which illustrates the element information item(s) involved,
followed by a tabulation of the correspondence between properties of the component
and properties of the information item. Where context may determine which of
several different components may arise, several tabulations, one per component,
are given. In the XML representation, bold-face
attribute names (e.g. count below) indicate a required
attribute information item, and the rest are
optional. Where an attribute information item has an enumerated type
definition, the values are shown separated by vertical bars, as for
size below; if there is a default value, it is shown
following a colon. The allowed content of the information item is
shown as a grammar fragment, using the Kleene operators ?,
* and +. The property correspondences are normative, but
the illustration of the XML representation element information items is not.
XML Representation Summary:
example Element Information Item |
|
<example
count = integer
size = large | medium | small : medium>
Content: (child1 | child2*)
</example>
|
|
|
The following highlighting is used for non-normative commentary in
this document:
Issue (dummy):
A recorded issue.
Ed. Note:
Notes from the editors to themselves or the Working Group.
NOTE:
General comments directed to all readers.
2 Conceptual Framework
This chapter gives an overview of XML Schema: Structures at the level of its abstract data model. (Schema Component Details (§3) provides details on this model, and subsequent
chapters define
a normative representation in XML for the components of the model.)
Readers interested primarily in learning to write schema documents may wish to first read [XML Schema: Exposition] and then consult XML Representation of Schemas and Schema Components (§4), using the sections below as a guide to the underlying formal structure of the schema language.
2.1 Overview of XML Schema
An XML Schema
defines a set of schema-valid XML documents. At a minimum, it consists of type definitions
and element declarations. It
identifies a set of well-formed element information items (as defined
in [XML-Infoset]), and furthermore
may specify augmentations to those items and their descendants. This augmentation makes explicit information which may have
been implicit in the original document, such as default values for
attributes and elements and
the types of element and attribute information items.
The process of schema validation consists of determining
whether an element information item is a member of the set defined by an XML Schema, and if so of
adding any appropriate augmentations.
2.2 XML Schema Abstract Data Model
This specification builds on [XML] and
[XML-Namespaces]. The concepts and definitions used
herein regarding XML are framed at the abstract level of information
items as defined in [XML-Infoset]. By
definition, this use of the infoset provides a priori guarantees of well-formedness
(as defined in [XML]) and namespace
conformance (as defined in [XML-Namespaces]) for all candidates for schema-validity.
Just as [XML] and
[XML-Namespaces] can be described in terms of
information items, XML Schemas can be described in terms of an
abstract data model. In defining XML Schemas in terms of an abstract
data model, this specification rigorously specifies the information which
must be available to a conforming XML Schema processor. The abstract
model for schemas is conceptual only, and does not mandate any
particular implementation or representation of this information. To
facilitate interoperation and sharing of schema information, a
normative interchange format for schemas is described in XML Representation of Schemas and Schema Components (§4)
Ed. Note:
The datatype spec's use of the word "component" makes things somewhat confusing
next to this specification's use of the same word. Perhaps the terminology in the datatype spec should be revised?
[Definition:] Schema component is the generic term for the building blocks that comprise the abstract data model of the schema.
[Definition:]
An XML Schema is a
set of schema components. There are 12 kinds of
component in all, falling into three groups. The primary components
are as follows. They may have names, and (except for some element
declarations) may be independently accessed:
- Simple type definitions
- Complex type definitions
- Element declarations
The secondary components are as follows. Like the primary
components, they may have names and be independently accessed:
- Attribute group definitions
- Identity-constraint definitions
- Model group definitions
- Notation declarations
Finally, the "helper" components provide small parts of
other components; they are not independent of their context and
cannot be independently accessed:
- Annotations
- Attribute declarations
- Model groups
- Particles
- Wildcards
During validation, [Definition:] Declaration components are associated by
(qualified) name to information items being validated.
On the other hand, [Definition:] definition components define
internal schema components that can be used in other schema components.
[Definition:] Declarations and
definitions may have and be identified by names, which are NCNames as defined by [XML-Namespaces].
[Definition:] Several kinds
of component have a target namespace, which is either
null or a namespace URI, also as
defined by [XML-Namespaces]. The target
namespace serves to identify the namespace within which the
association between the component and its name exists. In the case of
declarations, this in turn determines the namespace URI of, for example, the element
information items it may validate.
NOTE:
At the abstract level, there is
no requirement that the components of a schema share a
target namespace. Any schema for use in
schema-validation of documents containing names from more than one namespace
will of necessity include components with different target namespaces. This contrasts with
the situation at the level of the XML Representation of Schemas and Schema Components (§4), in which each schema document contributes
definitions and declarations to a single target namespace.
Schema-validity, defined in detail in Conformance * (§6), is a
relation between information items and schema components. For example, an
attribute information item may be schema-valid with respect to an attribute
declaration, a list of element information items may be schema-valid with
respect to a content model, and so on. The following sections briefly
introduce the kinds of components in the
schema abstract data model, other major features of the abstract model, and how they contribute to the overall definition of
schema-validity.
2.2.1 Type Definition Components
The abstract model provides two kinds of type definition component: simple
and complex.
[Definition:] This specification uses
the phrase type definition in cases where no distinction
need be made between simple and complex types.
Type definitions form a hierarchy with a single root. First we describe characteristics of that
hierarchy, then provide an introduction to simple and complex type definitions themselves.
2.2.1.1 Type Definition Hierarchy
[Definition:] Except for a distinguished ur-type definition, every type definition is, by construction, either a
restriction, an extension of some other type definition. Collectively, the graph of these relationships forms a tree known as the Type Definition Hierarchy.
[Definition:] A type
definition whose
declarations or facets are in a one-to-one relation with those of another type
definition, with each in turn restricting the possibilities of the one it
corresponds to, is said to be a restriction.
The specific restrictions might include narrowed ranges or reduced
alternatives.
Members of a type, A, whose definition is a restriction of the definition of another type, B, are always members of type B as well.
[Definition:] A complex type definition
which allows element or attribute content in addition to that allowed by another type
definition is said to be an extension.
[Definition:] A distinguished ur-type
definition is present in each XML Schema, serving as the root of the type
definition hierarchy for that schema. The ur-type definition has
the unique characteristic that it can function as a complex or a
simple type definition, according to context.
Specifically, restrictions of the ur-type definition can
themselves be either simple or complex type definitions.
[Definition:] A type definition used as the
basis for an extension or
restriction is known as
the base type definition of that definition.
Ed. Note: Should use this as a target for other references
throughout the text.
2.2.1.3 Complex Type Definition
A complex type definition is a set of attribute declarations and a content type, applicable to the [attributes] and
[children] of an element information item respectively. The content type may require the [children] to be empty, to be a string which is schema-valid with respect to particular simple type or to contain element information items which is schema-valid with respect to a particular model group, with or without character information items as well.
Each is complex type definition is either a:
A
complex type which extends another does so by having additional content model
particles at the end of the other definition's content model,
or by having additional attribute declarations, or both.
NOTE:
This specification allows only appending, and not other kinds of
extensions. This decision
simplifies application processing required to cast instances from derived to
base type. Future versions may allow more kinds of extension, requiring more
complex transformations to effect casting.
See Complex Type Definition Details (§3.3) for the composition and
schema-validation contributions of complex type definition schema components, XML Representation of Complex Type Definition Schema Components (§4.4.3) for the XML representation of
complex type definitions and Complex Type Definition Constraints (§6.3.11) for constraints on complex
type definition components as such.
2.2.2 Declaration Components
There are three kinds of declaration component: element, attribute, and
notation. Each described in a section below. Also included is a discussion of element equivalence
classes, which is a feature provided in conjunction with element declarations.
2.2.2.1 Element Declaration
An element declaration is an association of a name with a type definition, either simple or
complex, an (optional) default value and a set of identity-constraint
definitions. The association is either global or scoped to a containing complex type definition. A
global element declaration with name 'A' is broadly comparable to a pair of
DTD declarations as follows, where the associated type definition
fills in the ellipsis:
<!ELEMENT A . . .>
<!ATTLIST A . . .>
Element declarations contribute to
schema-validity as part of model group validation, when their defaults and type components are checked against an element
information item with a matching name and namespace, and by triggering
identity-constraint definition validation.
See Element Declaration Details (§3.2) for the composition and
schema-validation contributions of element declaration schema components, XML Representation of Element Declaration Schema Components (§4.4.2) for the XML representation of
element declarations and Element Declaration Constraints (§6.3.2) for constraints on
element declaration components as such.
2.2.2.2 Element Equivalence Class
In XML 1.0, the name and content of an element must correspond exactly to the element type referenced in the corresponding content model.
[Definition:] Through the new mechanism of element equivalence classes, XML Schemas provides a more powerful model supporting substitution of one named element for another.
Any global element declaration can serve as the defining element, or
exemplar, for an element equivalence class. Other global element declarations, regardless of target namespace, can be designated as members of the class defined by the exemplar. In a suitably enabled content model, a reference to the exemplar validates not just the exemplar itself, but elements corresponding to any member of the equivalence class as well.
All such members must have type definitions which are either the same as the
exemplar's type definition or
restrictions or extensions of it.
Therefore, although the names of elements can vary widely as new
namespaces and members of the equivalence class are defined, the
content of member elements is strictly limited according to the type
definition of the equivalence class exemplar.
Note that element equivalence classes are not represented as separate components. They are
specified in the property values for element declarations (see Element Declaration (§2.2.2.1)).
2.2.2.3 Attribute Declaration
An attribute declaration is an association between a name and a simple type definition, together
with occurrence information and (optionally) a default value. The
association is local to its containing complex type definition. Attribute declarations contribute to
schema-validity as part of complex type definition validation, when their
occurrence, defaults and type components are checked against an attribute
information item with a matching name and namespace.
See Attribute Declaration Details (§3.1) for the composition and
schema validation contributions of attribute declaration schema components, XML Representation of Attribute Declaration Schema Components (§4.4.1) for the XML representation of
attribute declarations and Attribute Declaration Constraints (§6.3.1) for constraints on
attribute declaration components as such.
2.2.3 Model Group Components
The model group, particle, and wildcard components contribute to
the portion of a complex type definition that controls an element
information item's content type.
2.2.3.1 Model Group
A model group is a constraint in the form of a grammar fragment that applies to
lists of element information items. It consists of a list of particles, i.e.
element declarations, wildcards and model groups. There are three varieties of
model group:
- Sequence (the element information items
match the particles in sequential order)
- Conjunction (the element information items match the
particles, in any order)
- Disjunction (the element information items match
one of the particles)
See Model Group Details (§3.6) for the composition and
schema-validation contributions of model group schema components, Complex Type Definition Details (§3.3) for the use of model groups as content models, XML Representation of Model Group Schema Components (§4.4.6) for the XML representation of
model groups and Model Group Constraints (§6.3.7) for constraints
on model group components as such.
2.2.3.2 Particle
A particle is a term in the grammar for element content, consisting of either an element
declaration, a wildcard or a model group, together with
occurrence constraints. Particles contribute to
schema-validity as part of complex type validation, when they allow anywhere
from zero to many element information items or sequences thereof, depending on
their contents and occurrence
constraints.
[Definition:] A particle can
be used in a complex type definition to express a validity
constraint on the [children] of an element information item; such a particle is called
a content model.
NOTE:
XML Schema: Structures content models are similar to but more expressive than
[XML] content models; unlike [XML], XML Schema: Structures applies content models to the validation of both mixed and element-only content.
See Particle Details (§3.7) for the composition and
schema-validation contributions of particle schema components, XML Representation of Model Group Schema Components (§4.4.6) for the XML representation of
particles and Particle Constraints (§6.3.10) for constraints
on particle components as such.
2.2.4 Identity-constraint Definition Components
A identity-constraint definition is an association between a name and one of
several varieties of
identity-constraint related to uniqueness and reference. All the
varieties use [XPath] expressions to pick out sets of
information items relative to particular target element
information items which are unique, or a key, or a valid reference, within
a specified scope. An element information item is only schema-valid with
respect to an element declaration
with identity-constraint definitions if those definitions are all satisfied for all the descendants
of that element information item which they pick out.
See Identity-constraint Definition Details (§3.9) for the composition and
schema-validation contributions of identity-constraint definition schema components, XML Representation of Identity-constraint Definition Schema Components (§4.4.8) for the XML representation of
identity-constraint definitions and Identity-constraint Definition Constraints (§6.3.3) for constraints
on identity-constraint definition components as such.
2.2.5 Group Definition Components
There are two kinds of convenience definitions available for use
in reusing pieces of complex type definitions: model group definitions
and attribute group definitions.
2.3 Constraints and Contributions
The [XML] specification describes two kinds of
constraints on XML documents: well-formedness and
validity constraints. Informally, the well-formedness constraints
are those imposed by the definition of XML itself (such as the rules for the
use of the < and > characters and the rules for proper nesting of
elements), while validity constraints are the further constraints on document
structure provided by a particular DTD.
The preceding section focussed on schema-validity, that is
the constraints on information items which schema components supply. In fact
however this specification provides four different kinds of normative statements about schema
components, their representations in XML and their contribution to the
schema-validation of information items:
-
[Definition:] Constraint on Schemas
-
Constraints on the schema components themselves, i.e.
conditions components must satisfy to be components at all. Largely to be
found in Conformance * (§6).
-
[Definition:] Schema Representation Constraint
-
Constraints on the
representation of schema components in XML. Some but not all of these are expressed in (normative) DTD for Schemas (§B) and (normative) Schema for Schemas (§A). Largely to be
found in XML Representation of Schemas and Schema Components (§4).
-
[Definition:] Validity Contribution
-
Constraints expressed by schema components which information
items must satisfy to
be schema-valid. Largely to be
found in Schema Component Details (§3).
-
[Definition:] Schema Information Set
Contribution
-
Augmentations to post-schema-validation information sets
expressed by schema components, which follow
as a consequence of schema-validation.
Largely to be
found in Schema Component Details (§3).
Schema information set
contributions are not new. XML 1.0
validation augments the XML 1.0 information set in similar ways,
for example by
providing values for attributes not present in instances, and by implicitly
exploiting type information for normalisation or access.
(As an example of the latter case, consider the
effect of NMTOKENS on attribute whitespace, and the semantics of
ID and IDREF.) By including schema
information set contributions, this specification makes explicit some features
that XML 1.0 left implicit.
2.4 Conformance
This specification describes three levels of conformance for schema aware processors. The first is
required of all processors. Support for the other two will depend on the application environments
for which the processor is intended.
[Definition:] Minimally conforming processors must completely and
correctly implement the Constraints on
Schemas, Validity Contributions,
and Schema Information
Set Contributions contained in this specification.
[Definition:] Processors which accept
schemas in the form of XML documents as described in XML Representation of Schemas and Schema Components (§4) are
additionally said to provide conformance to the XML Representation of Schemas.
Such processors must, when processing schema documents, completely and
correctly implement all Schema Representation
Constraints in this specification, and must adhere exactly to the
specifications in XML Representation of Schemas and Schema Components (§4) for mapping the contents of such documents to schema components for use in validation.
NOTE:
By separating the conformance requirements relating to the concrete syntax of XML schema
documents, this specification admits processors
which validate using schemas stored in optimised binary
representations, dynamically created schemas represented as programming language data structures, or implementations in which particular schemas are compiled into executable code
such as C or Java. Such processors can be said to be minimally conforming but not necessarily in conformance to the XML Representation of Schemas.
[Definition:] Fully conforming
processors are network-enabled processors which support both levels of conformance described
above, and which must additionally be capable of accessing
schema documents from the World Wide Web according to Representation of Schemas on the World Wide Web (§2.7) and XXX.
.
Ed. Note:
A a reference to the rules for handling
schema location, dereference of namespace Uris, etc.
NOTE: Although this specification provides just these three standard levels of conformance, it is
anticipated that other conventions can be established in the future. For example, the World Wide
Web Consortium is considering conventions for packaging on the Web a variety of
resources relating to individual documents and namespaces. Should such
developments lead to new conventions for representing schemas, or for accessing them on the Web,
new levels of conformance can be established and named at that time. There is no need to modify
or republish this recommendation to define such additional levels of conformance.
2.5 Names and Symbol Spaces
As discussed in XML Schema Abstract Data Model (§2.2), most schema
components (may) have names.
If all such names were assigned from the same "pool", then
it would be impossible to have, for example, a simple type definition and an element
declaration both with the name
"title" in a given target namespace.
This specification
therefore introduces the term
[Definition:] symbol space to represent a
collection of names, each of which is unique with respect to the others. A symbol space is similar to the non-normative concept of namespace partition introduced in [XML-Namespaces].
There is a single distinct symbol space within a given target
namespace for each kind of definition and declaration component
identified in XML Schema Abstract Data Model (§2.2), except that within a target namespace, simple
type definitions and complex type definitions share a symbol space.
Within a given symbol space, names are unique, but the same name may appear in more than one symbol space without conflict. For example, the same name can appear in both a type definition and an element declaration, without conflict or necessary relation between the two.
Attribute declarations and locally scoped element
declarations are special with regard to symbol spaces.
Every complex type definition defines its own attribute declaration
symbol space and local element declaration symbol
space, where these symbol spaces are distinct from each other and from any of the other
symbol spaces. So, for example, several complex type definitions having
the same target namespace can contain
an attribute declaration for the unqualified name "priority", or contain a local element declaration
for the name "address", without conflict or necessary relation between
the two.
2.6 Schema-Related Markup in
Documents Being Schema-Validated
The XML representation of schema components uses a vocabulary
identified by the namespace URI http://www.w3.org/1999/XMLSchema.
XML Schema: Structures also defines several attributes for direct use in XML documents. These attributes are in a different namespace,
which has the namespace URI http://www.w3.org/1999/XMLSchema/instance.
For brevity, the text and examples in this specification use the prefix
xsi: to stand for this latter namespace; in practice,
any prefix can be used.
2.6.2 xsi:null
XML Schema: Structures introduces a distinguished null value for XML document elements. An
element has the null value if it has no [children] and carries the attribute xsi:null.
Ed. Note:
Are other attributes allowed? Must sync with validation rules.
2.6.3 xsi:schemaLocation
The xsi:schemaLocation attribute can be used in a document to provide
hints as to the physical location of schema documents to be used for validation.
3 Schema Component Details
The following sections provide full details on the properties and
significance of each kind of schema component. For each property, its range,
that is the kinds of values it may have, is defined. This can be understood as
defining a schema as a labelled directed graph, where every vertex is a schema
component or a literal (string, boolean, number) and every labelled edge a property. Any property not
identified as optional is required to be present, optional properties which are absent are taken to have null as their value. Any
property identified as a having a set, subset or list value may have an empty value unless this is explicitly
ruled out: this is not the same as null. Any property value identified as subset of some set may be equal to that set, unless a proper subset is explicitly called for.
By 'string' here and below is meant a
sequence of ISO 10646 character codes identified as legal XML character codes
in [XML].
Ed. Note:
Or the UNICODE 3 addendum, where/when?
Throughout the following sections, when we refer to the [value] of some
attribute information item, we mean by this a string composed of, in order, the
[character code] of each character information item in the [children] of that
attribute information item.
Many properties of schema components are identified below as having
other schema components as values. For the purposes of exposition, the definitions in
this section assume that (unless the property is explicitly identified as
optional) all such values are in fact present. When schema
components are constructed from XML representations involving reference by name
to other components, this assumption may be violated if one or more references
cannot be discharged. This specification addresses the matter of missing
components in a uniform manner, described in Missing Sub-components (§6.2): no mention of
handling missing components will be found in the individual component
descriptions below.
NOTE:
Schema components are an idealisation of the information a schema-aware
processor requires: implementations are not constrained in how they provide
it. In particular, no implications about literal embedding versus indirection
follow from the use above of language such as "properties . . . having . . .
components as values".
NOTE:
Readers whose primary interest is in the XML representation of schemas
may wish to skip this chapter on the first reading, concentrating on XML Representation of Schemas and Schema Components (§4) and [XML Schema: Exposition].
Ed. Note:
Due to time constraints in preparing this draft, the {annotation} properties are not explicitly described for the
components below. In all cases, the property is an annotation
(see "Annotation Details" below).
3.1 Attribute Declaration Details
Attribute declarations provide for:
- Requiring/preventing the appearance of attribute information items;
- Constraining attribute information item values by a simple type definition;
- Providing default or fixed values for an attribute information item.
The attribute declaration schema component has the following
properties:
The {name} property must match the local part of the names of attributes being validated.
A "qualified" attribute name is one that appears with a namespace prefix which is itself declared with a
value other than the empty string. A non-null value of the {target namespace} property provides for validation of
such attributes qualified with an identical namespace URI. Null values of {target namespace} provide for validation of local
(unprefixed) attributes. Each complex type definition provides its own symbol space for the
names of its associated local attribute declarations. (E.g. an attribute
named title within one type definition need not have the same
simple type definition as one declared within another complex
type; neither of these need agree with the declaration for a similarly named qualified attribute.)
A {min occurs} of 1 specifies that the corresponding attribute must
be present; a value of 0 allows for optional attributes.
Similarly, a {max occurs} of 0 indicates an attribute that must
not be present; a value of 1 (the normal case) allows the attribute to occur
explicitly.
The value of the attribute must conform to the supplied {simple type definition}.
{value constraint} reproduces the functions of XML 1.0 default and #FIXED
attribute values. fixed indicates that the attribute value must match the supplied
constraint string; default specifies that the attribute is to appear unconditionally in
the post-schema-validation information set, with the supplied value used
whenever the attribute is not actually present.
NOTE: A more complete and formal presentation of the semantics of {name}, {target namespace},
{min occurs}, {max occurs} and
default {value constraint} is provided in
conjunction with other aspects of complex type validation (see Element Children and Attributes Valid (§3.3).)
[XML-Infoset] distinguishes namespace declarations such as xmlns or xmlns:xsl from
attributes. Accordingly, it is unnecessary and in fact not possible for
schemas to contain attribute declarations corresponding to such
namespace declarations, see xmlns Not Allowed (§6.3.1). No means is provided to supply a
default value for a namespace declaration.
See XML Representation of Attribute Declaration Schema Components (§4.4.1) for the XML representation of
attribute declarations and Attribute Declaration Constraints (§6.3.1) for constraints on attribute
declaration components as such.
Validation Contribution: Attribute Valid
For an attribute information item to be schema-valid with respect to an
attribute declaration, its
[value] must
Schema Information Set Contribution: Attribute Type
In the post-schema
validation infoset a
[schema type] property is added to the attribute information item with the
{simple type definition} as its value.
3.2 Element Declaration Details
Element declarations provide for:
- Establishing the validity of element information items.
- Determining schema information set contributions, such as default values.
- Establishing uniquenesses and reference constraint relationships among the values of related elements and
attributes.
- Controlling the substitutability of elements through the
mechanism of element equivalence classes.
The element declaration schema component has the following
properties:
The {name} property must match the local part of the names
of elements being validated.
A {scope} of global declares elements available for use in content
models throughout the schema. Locally scoped elements are available for use only within the
complex type identified by the {scope} property. For globally scoped element declarations, a non-null value of the {target namespace} property provides for validation of
namespace qualified elements. Null values of
{target namespace} validate unqualified elements, including
locally scoped elements. This property is also null in the case of non-global declarations within named model groups: their scope will be determined when they are used in the construction of complex type definitions.
An element is schema-valid
if it obeys the schema validity constraints of the {type definition}. For such an
element, the schema information set contributions from the {type definition} are applied to the
corresponding element information item in the post-schema-validation information set. {type definition} must not be an
abstract type definition.
If {nullable} is true, then the element is also schema valid if it has
no text or element content, and
carries the namespace qualified attribute with [local name] null from namespace http://www.w3.org/1999/XMLSchema/instance (see xsi:null (§2.6.2)). Formal details of element validation are described in Element Valid (Explicit) (§3.2).
{value constraint} establishes a default or fixed value for an element. If default is specified, and if the element
being validated is empty, then the supplied
constraint string becomes [character]
[children] of the validated element in the post-schema-validation
infoset. If fixed is specified, then the element's content
must either be empty, in which case fixed behaves as default,
or it must match the supplied constraint string.
{identity-constraint definitions} express constraints establishing uniquenesses and reference relationships among the values of related elements and
attributes. See Identity-constraint Definition Details (§3.9).
Element declarations are members of the equivalence class, if any, identified
by {equivalence class affiliation}. Membership is transitive; an element
declaration is implicitly a member of any class of which its {equivalence class affiliation} is a member.
An empty {equivalence class exclusions} creates an equivalence
class admitting other element declarations having the same {type definition} or
types derived therefrom. The explicit
values of {equivalence class exclusions} exclude from the equivalence class elements having types which
are extensions, lists, restrictions or reproductions respectively of {type definition}. If all values are specified, then no equivalence class is possible based on this element declaration.
The supplied values for {disallowed substitutions} determine
whether an element declaration appearing in a content model will be prevented from additionally
validating elements (a) with an xsi:type (§2.6.1) that identifies an
extension, list, restriction and/or reproduction of the type of the declared element, and/or (b) from validating elements which are in the same
equivalence class (equivClass) as the declared element.
If {disallowed substitutions} is empty, then all derived types and equivalence class members are valid.
Element declarations for which {abstract} is true can appear in
content models only when equivalence class substitution is allowed;
such declarations may not themselves ever be used to validate element content.
See XML Representation of Element Declaration Schema Components (§4.4.2) for the XML representation of
element declarations and Element Declaration Constraints (§6.3.2) for constraints on element
declaration components as such.
Validation Contribution: Element Valid (Explicit)
An element information item is schema-valid with respect to an
element declaration if
| 1.1 |
If {nullable} is false there is no attribute information item among the element
information item's [attributes] whose [namespace URI] is identical to http://www.w3.org/1999/XMLSchema/instance and whose [local name] is null;
|
| 1.2 |
If {nullable} is true and there is such an attribute
information item and its [value] is true, then
| 1.2.1 |
the element information item must have no character or element information item
[children];
|
| 1.2.2 |
there is no fixed {value constraint}.
|
|
If there is an attribute information item among the element
information item's
[attributes] whose
[namespace URI] is identical to
http://www.w3.org/1999/XMLSchema/instance and whose
[local name] is
type, then
[Definition:] We refer below to the
actual type definition. If the above three clauses obtain, this
should be understood as referring to the local type
definition, otherwise to the {type definition}.
If the declaration has a
{value constraint}, then
provided clause 1.2 has not obtained
Otherwise (the element information item has character information item
[children] or there is no
{value constraint}) if the
actual type definition is a simple type
definition, then
otherwise (the
actual type definition is a complex type
definition)
Issue (nullRequiresEmpty):
Is it a precondition for being nullable that the element's contentType
allow no content? If not, then more needs to be said in Chapter 6, if so, this needs
to be spelled out.
Ed. Note: The above also allows null elements to have
attributes, i.e. it's their CONTENT which is null. Was that the
designers' intention? See related ednote under xsi:null in chapter 2.
NOTE: The {name} and {target namespace} properties are not
mentioned above because they are checked during particle validation, as per
Element Sequence Valid (Particle) (§3.7).
Schema Information Set Contribution: Element Default Value
If the
{value constraint} is present and the element
information item has no character or element information item
[children], the post-schema
validation infoset has a list of character information items, one per character
in the
{value constraint} string, appended to its
[children].
Ed. Note:
Should we add a property to indicate THAT the value was supplied by default?
Schema Information Set Contribution: Element Type
In the post-schema
validation infoset a
[schema type] property is added to the element information item with the
actual type definition as its value.
Schema Information Set Contribution: Element Null
If clause 1.2 of
Element Valid (Explicit) (§3.2) above obtains, in the post-schema
validation infoset a
[null] property is added to the element
information item with the value true.
3.3 Complex Type Definition Details
Complex Type Definitions provide for:
- Constraining element information items by providing Attribute Declaration (§2.2.2.3)s governing the appearance and content of
[attributes]
- Constraining element information item [children] to be empty, or to conform to a specified element-only or mixed content model.
- Using the mechanisms of Type Definition Hierarchy (§2.2.1.1) to derive a complex type from another simple or complex type.
-
Specifying contributions to the post-schema-validation information set for elements.
- Limiting the ability to derive additional types from a given complex type.
- Controlling the permission to substitute, in an instance, elements of a derived
type for elements declared in a content model to be of a given complex type.
- Determining post-schema-validation
information set contributions.
A complex type definition schema component has the following
properties:
Complex types are identified by their {name} and {target namespace}. Except
for anonymous complex types (those with no {name}), complex
type definitions must be uniquely identified within an XML
Schema. Complex type {name}s and {target namespace}s
are provided for reference from
instances (see xsi:type (§2.6.1)), and for use in the XML Representation of Schemas and Schema Components (§4)
(specifically in element and attribute). See References to schema components across namespaces (§5.2.2) for the use of component
identifiers when importing one schema into another.
NOTE:
The {name} of a complex type is not ipso
facto the [(local) name] of the
element information items validated by that definition. The connection between a
name and a type definition is described in Element Declaration Details (§3.2).
As described in Type Definition Hierarchy (§2.2.1.1), each complex type is derived from a
{base type definition} which is itself either a Simple Type Definition (§2.2.1.2) or a Complex Type Definition (§2.2.1.3). {derivation method} specifies the means of derivation as either extension or restriction (see Type Definition Hierarchy (§2.2.1.1)).
A complex type with an empty specification for {final} can be used as a
{base type definition} for other types derived by any of
extension, restriction or reproduction; the explicit values extension,
restriction and reproduction prevent further
derivations by extension, restriction and reproduction respectively. If all values are specified, then the complex type is said to be
[Definition:] final: no
further derivations are possible.
A complex type for which {abstract} is true must not appear as the
{type definition} of an Element Declaration (§2.2.2.1), and must not be referenced from an
xsi:type (§2.6.1) attribute in an instance document; such abstract complex types can be
used as {base type definition}s, but they are never used directly to validate
element content.
{attribute declarations} are a set of individual Attribute Declaration (§2.2.2.3)s
to be used for schema-validating the
[attributes]
of element information items. See Element Children and Attributes Valid (§3.3)
and Attribute Valid (§3.1) for details of attribute validation.
{attribute wildcard}s provide a more flexible specification for validation of
attributes not explicitly included in {attribute declarations}.
Informally, the specific values
of {attribute wildcard} are interpreted as follows:
-
any: [attributes] can include attributes with any qualified or unqualified name.
-
a set whose
members are either namespace URIs or null: [attributes] can
include any attribute(s) from the specified namespace(s). If null is included in the set, then any unqualified attributes are (also) allowed.
-
'not' and a namespace URI: [attributes] cannot include attributes from the specified namespace.
-
'not' and null: [attributes] cannot include
unqualified attributes.
See Element Children and Attributes Valid (§3.3) and Wildcard allows Namespace URI (§3.8) for formal
details of attribute wildcard validation.
{content type} determines the schema-validation of [children] of element information items. Informally:
{prohibited-substitutions} determine
whether an element declaration appearing in a
content model is prevented from additionally
validating elements with an xsi:type (§2.6.1) attribute that
identifies an extension, restriction or reproduction of the type of the declared element.
If {prohibited-substitutions} is empty,
then all such substitutions are valid.
See Element Children and Attributes Valid (§3.3)
for a formal specification of element content validation.
See XML Representation of Complex Type Definition Schema Components (§4.4.3) for the XML representation of
complex type definitions and Complex Type Definition Constraints (§6.3.11) for constraints on
complex type definition components as such.
Validation Contribution: Element Children and Attributes Valid
An element information item is schema valid with respect to a complex type definition if:
Schema Information Set Contribution: Attribute Default Value
There is a complex type definition version of the ur-type definition present in every
schema by definition. It has the following properties:
| Complex Type Definition of the Ur-Type |
|
|
Ed. Note:
This should be handled with a generic tableau markup
The mixed content specification together with the
unconstrained wildcard content model and attribute specification produce the defining property for the
complex ur-type definition, namely that every complex type definition is
either an extension of a simple type definition or (eventually) a restriction
of the complex ur-type definition: its permissions and requirements are
the least restrictive possible.
3.6 Model Group Details
When the [children] of element information items are not constrained
to be empty or by reference to a simple type definition
(Simple Type Definition Details (§3.12)), the sequence of element
information item [children] content may be specified in
more detail with a model group. Because the {term} property of a particle can be a
model group, and model groups contain particles, model groups can indirectly contain other model groups; the grammar for content models
is therefore recursive.
The model group schema component has the following
properties:
{compositor}determines whether the element
information item [children] validated by the model group must:
- (sequence) correspond, in order, to the specified {particles};
- (choice) corresponded to exactly one of the specified {particles};
- (all, (in which case {particles} is restricted to contain local and global element
declarations, with minOccurs=maxOccurs=1) contain exactly one of each element specified in {particles}. The elements can occur in any order.
{annotation}Description to be supplied in a future draft.
Validation Contribution: Element Sequence Valid
[Definition:] We define a
partition of a sequence as a sequence of sub-sequences, some or
all of which may be empty, such that concatenating all the sub-sequences yields
the original sequence.
A sequence (possibly empty) of element information items is schema-valid with respect to
a model group if
or
or
Nothing in the above should be understood as ruling out groups whose
{particles} is empty: although no sequence can be schema-valid
with respect to such a group whose
{compositor} is
choice, the empty sequence
is schema valid with respect
to empty groups whose
{compositor} is
sequence or
all.
NOTE:
The above definition is implicitly non-deterministic, and should not be
taken as a recipé for implementations. Note in particular that when {compositor} is all, particles is restricted to a list of local and global element declarations (see Model Group Constraints (§6.3.7)). A much simpler implementation is possible for than would arise from a literal interpretation of the definition above; informally, the content is valid when each declared element occurs exactly once, and each is valid with respect to its corresponding declaration. The elements can occur in arbitrary order.
Ed. Note:
The above depends on chapter 6 to rule out 'all' except
directly within content type.
See XML Representation of Model Group Schema Components (§4.4.6) for the XML representation of
model groups and Model Group Constraints (§6.3.7) for constraints
on model group components as such.
3.7 Particle Details
As described in Model Group Details (§3.6), particles contribute to the definition
of content models. The particle schema component has the following properties:
The following is an informal overview of the properties of a particle. Formal interpretation of
these properties is found in Element Sequence Valid (Particle) (§3.7).
In general, multiple element
information item [children], possibly with intervening character [children] if the content type
is mixed, can be validated with respect to a single particle. {min occurs} determines the minimum number of such element [children] that can validly occur. The number of such children must be greater than or equal to {min occurs}. If {min occurs} is 0, then occurrence of such children is optional.
The number of such element [children] must be less than or equal to any numeric specification of
{max occurs}; if {max occurs} is *, then there is no
upper bound on the number of such children.
{nullable}, {disallowed substitutions} and {value constraint}, if
specified, merge with the corresponding properties of the supplied element declaration.
Validation Contribution: Element Sequence Valid (Particle)
A sequence (possibly empty) of element information items is schema-valid
with respect to a particle if
| 1.1 |
The length of the sequence is greater than or equal to the {min occurs};
|
| 1.2 |
The length of the sequence is less than or equal to the {max occurs};
|
| 1.3 |
Either
or
or
| 1.3.3.1 |
the {term} is an element declaration;
|
| 1.3.3.2 |
for each element
information item in the sequence either
or
or
|
|
See XML Representation of Model Group Schema Components (§4.4.6) for the XML representation of
particles and Particle Constraints (§6.3.10) for constraints
on particle components as such.
3.8 Wildcard Details
A wildcard provides for validation of element information items dependent on their namespace
URI, but independently
of their local name. The wildcard schema component has the following properties:
Ed. Note:
missing the processContents property, and a descriptions of the
processing options for material allowed by an any, i.e. strict (must validate,
find the defs and decls you need or invalid; lax, i.e. validate when you can
find the defs and decls, OK if you can't; skip, i.e. don't try, call it valid
no matter what.
{namespace constraint} provides for validation of elements that:
-
(any) have any namespace or are not namespace qualified;
-
(not and a namespace URI) have any namespace other than the specified namespace URI, or
are not namespace qualified;
-
(not and null) are namespace qualified;
-
(a set whose
members are either namespace URIs or null) have any of the
specified namespaces and/or, if null is included in the set, are unqualified.
Validation Contribution: Element Valid (Wildcard)
Validation Contribution: Wildcard allows Namespace URI
A value which is either a namespace URI or
null is schema valid with respect to a wildcard constraint (the
value of a
{namespace constraint} or a
{attribute wildcard}) if
| 1.1 |
the constraint is any;
|
or
| 1.2 |
the constraint is a pair of not and a namespace URI, and
the value is not identical to the namespace URI;
|
or
| 1.3 |
the constraint is a set, and the value is identical to one of the members of the set.
|
See XML Representation of Wildcard Schema Components (§4.4.7) for the XML representation of
wildcards and Wildcard Constraints (§6.3.5) for constraints
on wildcard components as such.
3.9 Identity-constraint Definition Details
Identity-constraint definition components provide for uniqueness and reference constraints with respect
to the contents of multiple elements and attributes. The identity-constraint definition schema component has the following
properties:
Identity-constraint definitions are identified by their {name} and {target namespace}; Identity-constraint definition identities must be unique within an XML Schema. See References to schema components across namespaces (§5.2.2) for the use of component
identifiers when importing one schema into another.
Informally, {identity-constraint category} identifies the Identity-constraint definition as playing one of
three roles:
- (unique) the Identity-constraint definition asserts uniqueness, with respect to the content
identified by {selector}, of the tuples resulting from evaluation of the {fields} Xpath(s).
-
(key) the Identity-constraint definition asserts uniqueness as for
unique. key further asserts that all selected content
actually has such tuples.
- (keyref) the Identity-constraint definition asserts a correspondence, with respect to the content
identified by {selector}, of the tuples resulting from evaluation of the {fields} Xpath(s), with those of the {referenced key}.
These constraints are specified independently of the types of the
attributes and elements involved, i.e. something declared as of type integer
may also serve as a key, unlike ID and
IDREF. Each constraint declaration has a name, which exists in a
single symbol space for constraints.
Overall the augmentations to XML's ID/IDREF mechanism are:
- Not just attribute values, but also element content and combinations
of values and content can be declared to be unique;
- Constraints are specified to hold within the scope of particular elements;
- (Combinations of) attribute values and/or element content can be
declared to be keys, that is, not only unique, but always present and non-nullable;
-
The comparison between keyref {fields} and
key or unique {fields} is by value equality,
not by string equality, so that a decimal
0.5 will match a decimal .5.
{selector} specifies an XPath expression [XPath] relative to
instances of the element being declared. This must identify a node set of subelements (i.e. elements contained within the declared element) to which the constraint applies.
{fields} specifies XPath expressions relative to each
element selected by a {selector}. This must identify
a single node (element or attribute, not necessarily within the selected element) whose content or value, which must be
of a simple type, is used in the constraint. It is possible to specify an
ordered list of {fields}s, to cater to multi-field keys,
keyrefs, and uniqueness constraints.
NOTE:
Provision for multi-field keys etc. goes beyond what is supported by xsl:key.
Issue (restrictConstrXPaths):
XPath expressions can take arbitrarily complicated forms and it is unnecessary to burden
XML Schema implementations with supporting every feature of XPath. The XPaths
in {selector} and {fields} should be restricted to certain specified simple forms.
The WG has asked the editor to bring forward a proposal. Here's the
starting point, feedback invited:
- |, /, //, .., @QName, QName, *, ancestor::, []
- or, and, =
- the not, name and position functions
- string and number literals
- prefixes interpreted per in-scope namespace declarations
Issue (islandValidConstraint):
What are the interactions between identity-constraints and opportunistic
validation inside wildcards?
A formal description of Identity-constraint definition validation is given below in Identity-constraint Satisfied (§3.9)
Validation Contribution: Identity-constraint Satisfied
An element information item is schema-valid with respect to a identity-constraint if
| 1.1 |
The {selector}, with the element information item as the
context node, evaluates to a node-set (as defined in
[XPath]). [Definition:] Call this the target node set;
|
| 1.2 |
Each node in the target node set is an
element node;
|
| 1.3 |
For each node in the target node set all of the {fields}, with that node as the context
node, evaluate to either an empty node-set or a node-set with exactly one
member. [Definition:] Call the sequence of the values (as defined in [XML Schemas: Datatypes]) of those node-sets in order the key-sequence of the node;
|
[Definition:] Call the subset of the target node set for
which all the {fields} evaluate to a node-set with exactly one
member which is an element or attribute node the qualified node set;
or
or
| 2.3.1 |
The {identity-constraint category} is keyref;
|
| 2.3.2 |
For each member of the qualified node
set (call this the keyref member), there must be a member of the node table associated with the
{referenced key} in the [identity-constraint table]
of the element information item (see Identity-constraint Table (§3.9), which must be
understood as logically prior to this clause of this constraint, below) whose
key-sequence is equal to the
keyref member's key-sequence member for member.
|
| 2.3.3 |
Ed. Note:
The fields cardinality of a keyref must be equal to the fields
cardinality of its [referenced key], checked in chapter 6.
Ed. Note:
This is simpler (and in one respect, the hyper-uniqueness implied by
the uniqueness requirement built in to the merger of the tables defined below, stronger) recursive descent implied than the apparently agreed design: is it acceptable for
v.1, as I don't see how to do better?
|
Ed. Note:
Check the resolution of the nested domains issue -- is the above
correct wrt that?
Schema Information Set Contribution: Identity-constraint Table
[Definition:] An eligible
identity-constraint of an element information item is one such that clauses 2.1.[1-2] or 2.2.[1-3] of Identity-constraint Satisfied (§3.9) obtains
with respect to that item and that constraint,
or such that any of the element information item [children] of that item have a
[identity-constraint table] with an entry for that constraint.
[Definition:] A node table is a set of pairs each consisting of
a key-sequence and an element node.
Whenever an element information item has one or more
eligible constraints, a new
[identity-constraint table] is added to the post-schema-validation
infoset for that element information item, consisting of pairs of identity-constraints
and
node tables, one for each of the item's
eligible constraints, with the
node table in each pair defined as follows: There is a member in the
node table
associated with an
eligible constraint of an
element information item consisting of a
key-sequence (call it
k) and a node (call it
n) if and only if
Ed. Note:
This is considerably less than transparent. The intention is to
recursively construct r-c tables at one level by merging the still-unique
members of each corresponding table one level down, if any, with the new
entries arising from evaluating the r-c at this level, if any, throwing out any which conflict.
See XML Representation of Identity-constraint Definition Schema Components (§4.4.8) for the XML representation of
identity-constraint definitions and Identity-constraint Definition Constraints (§6.3.3) for constraints
on identity-constraint definition components as such.
3.10 Notation Declaration Details
Ed. Note: Cleanup of the descriptive text below, and descriptions of individual properties to be provided in a
future draft.
The notation declaration schema component has the following
properties:
Notation declarations do not participate in schema-validation as such.
They are referenced in the course of schema-validating strings as members of
the NOTATION simple type.
See XML Representation of Notation Declaration Schema Components (§4.4.9) for the XML representation of
notation declarations and Notation Constraints (§6.3.8) for constraints on
notation declaration components as such.
3.11 Annotation Details
Ed. Note: Cleanup of the descriptive text below, and descriptions of individual properties to be provided in a
future draft.
The annotation schema component has the following
properties:
Annotations do not participate in schema-validation as such. Provided
an annotation itself satisfies all relevant Constraints of Schemas it cannot affect the schema-validity of element information items.
See XML Representation of Annotation Schema Components (§4.4.10) for the XML representation of
annotations and Annotation Constraints (§6.3.9) for constraints
on annotation components as such.
3.12 Simple Type Definition Details
Simple type definitions provide for constraining character information item [children] of element and attribute
information items.
The simple type definition schema component has the following properties:
Simple types are identified by their {name} and {target namespace}. Except
for anonymous simple types (those with no {name}), simple
type definitions must be uniquely identified within an XML
Schema. Simple type {name}s and {target namespace}s
are provided for reference from
instances (see xsi:type (§2.6.1)), and for use in the XML Representation of Schemas and Schema Components (§4)
(specifically in element and attribute). See References to schema components across namespaces (§5.2.2) for the use of component
identifiers when importing one schema into another.
NOTE:
The {name} of a simple type is not ipso
facto the [(local) name] of the
element or attribute information items validated by that definition. The connection between a
name and a type definition is described in Element Declaration Details (§3.2) and Attribute Declaration Details (§3.1).
A simple type definition for which {abstract} is true must not appear as the
{type definition} of an Attribute Declaration (§2.2.2.3), must not be used as the {base type definition} of an enumeration simple type, must not used as the {base type definition} of a list simple type, and must not be referenced from an
xsi:type (§2.6.1) attribute in an instance document.
{variety} determines whether the simple type corresponds to an
atomic, enumeration, or list type as defined by [XML Schemas: Datatypes].
A simple type with an empty specification for {final} can be used as a
{base type definition} for other types derived by restriction; and/or as the
{base type definition} of an enumeration simple type, and/or as the {base type definition} of a list simple type. The explicit values restriction,
enumeration and list prevent any or all of those uses respectively.
Ed. Note:
Need to describe 'reproduction' value.
As described in Type Definition Hierarchy (§2.2.1.1), every atomic simple type definition is
a restriction of some other simple
{base type definition}, which is itself either a simple type definition or the ur-type definition. Each atomic type is ultimately a restriction of (or identical to) exactly one built in simple {primitive type definition}.
{facets} for each atomic simple type definition are selected from those defined in
[XML Schemas: Datatypes] for
the corresponding {primitive type definition}. Therefore, the value
space and lexical space (I.e. the content validated by) any atomic simple type is determined by the
pair {{primitive type definition}, {facets}}.
Enumeration simple types are restrictions
of the specified {base type definition}; enumeration types validate only
content that matches one of the specified {strings}.
As specified in [XML Schemas: Datatypes], list simple types validate whitespace separated tokens, each of
which conforms to the specified {base type definition}. The base type specified
must not itself be a list type, and must be one of the types identified in [XML Schemas: Datatypes] as a
suitable base for a list simple type.
Ed. Note:
Careful readers will observe that the above specification of list types conflicts
with the claim in
"Type Derivation" that all simple types are restrictions of other simple types.
This anomaly has no effect on the validation of content, but it does affect the
cleanliness of the
hierarchy exposed by a post-schema validation infoset, which includes simple type
definitions derived by list-formation as well as restriction.
Simple type definitions for all the built-in primitive datatypes, namely string, boolean, float,
double, decimal, timeInstant, timeDuration,
recurringInstant, binary, uri (see the Primitive
Datatypes section of [XML Schemas: Datatypes]), as well as for the
ur-type definition (as previously described), are present by definition in every schema. All
are in the XML Schema {target namespace} (namespace URI http://www.w3.org/1999/XMLSchema), have an atomic {variety} with an empty
{facets} and the ur-type definition as
their {base type definition} and themselves as {primitive type definition}.
Similarly, simple type definitions for all the built-in derived
datatypes (see the Derived
Datatypes section of [XML Schemas: Datatypes]) are present by definition in every schema, with
properties as specified in [XML Schemas: Datatypes] and as represented in XML in the schema for
datatypes
therein.
There is no separate ur-Type for simple types. As discussed in
Type Definition Hierarchy (§2.2.1.1), the ur-type definition functions as a simple type when used as the base type definition for a simple type.
Validation Contribution: String Valid
A string is schema valid with respect to a simple type definition if
See XML Representation of Simple Type Definition Schema Components (§4.4.11) for the XML representation of
simple type definitions and Simple Type Definition Constraints (§6.3.12) for constraints on simple
type definition components as such.
4 XML Representation of Schemas and Schema Components
The principal purpose of XML Schema: Structures is to define a set of
schema components that constrain the contents of instances and augment the
information sets thereof. Although no external representation
of schemas is required for this purpose, such representations will
obviously be widely used. To provide for this in an appropriate and
interoperable way, we specify a normative XML representation for schemas which
makes provision for every kind of schema
component. [Definition:] These may be
gathered together in to a single schema document, i.e. an XML
element information item. For the schema document as a whole, and
its constituents, the sections below define correspondences between element
information items (with declarations in
(normative) Schema for Schemas (§A) and (normative) DTD for Schemas (§B)) and
schema components. All the element information items in the XML representation
of a schema are in the XML Schema namespace, that is their [namespace URI] is http://www.w3.org/1999/XMLSchema. Although a common way of creating schema documents will be using an XML parser, this is not required: any mechanism which constructs conformant infosets as defined in [XML-Infoset] is a possible starting point.
Throughout the following sections, when we specify that a particular
property
of a schema component corresponds to the [value] of some attribute information item or the [children] of some element information item,
the value in question is understood to be based on a string consisting of the list, in order, of the
[character code] of each character information item in the [children] of that
attribute information item or in the [children] of that element information
item respectively, that string then being interpreted as appropriate to the
defined type of the property in question.
When we say that a numeric-valued property of a schema component
corresponds to the [value] of some attribute information item, the number in
question is understood to be the base 10 interpretation of string described above.
4.1 XML Representations of Schemas
A schema is represented in XML by one or more schema documents. A schema document contains representations for a collection of schema components, e.g. type definitions and element declarations, which have a common {target namespace}. A schema document which has one or more import element information items corresponds to a schema with components with more than one {target namespace}, see Schema Composition (§5.2.2).
There is no single schema component corresponding to a
schema element information item, and so no local correspondence of
attributes to properties is specified above. The blockDefault,
finalDefault and targetNamespace attributes
illustrated above are appealed to in the sub-sections below, as they provide
global information applicable to many representation/component correspondences. The
other attributes (id and version) are for user
convenience, and this specification defines no semantics for them.
The definition of the schema abstract data model in XML Schema Abstract Data Model (§2.2) makes clear that most components have a {target namespace}. Most components corresponding to representations within a given schema element information item will have a {target namespace} which corresponds to the targetNamespace attribute.
Since the empty string is a legal (relative) URI reference, supplying
an empty string for targetNamespace is not the same
as not specifying it at all. The appropriate form of schema document
corresponding to a schema whose components have no
{target namespace} is one which has no
targetNamespace attribute specified at all.
NOTE: The XML namespaces recommendation discusses only instance document syntax for
elements and attributes; it therefore provides no direct framework for managing
the names of type definitions, attribute group definitions, and so on. Nevertheless, we apply the target namespace facility uniformly to all
schema components, i.e. not only declarations but also definitions have a {target namespace}.
| Example |
<xs:schema
xmlns:xs="http://www.w3.org/1999/XMLSchema
targetNamespace="http://purl.org/metadata/dublin_core"
version="M.n">
...
</xs:schema>
|
|
| A modest beginning to a schema. |
|
Although the schema above might be a complete XML document, schema
need not be the document element, but can appear within other documents.
Indeed there is no requirement that a schema be derived from a (text) document
at all: it could be built 'by hand' via e.g. a DOM-conformant API.
Aside from annotation, which is not named and
corresponds to a "helper" schema component, and include and import, which do not correspond directly to any schema component at all, each of the element information
items which may appear in the content of schema corresponds to
a primary or secondary schema component, and in all cases these are named. The
sub-sections of XML Representation of Schema Components (§4.4)
present each such item in turn, setting out the
components to which it may correspond.
4.3 References to Schema Components
Reference to
schema components from a schema document is managed in a uniform way,
whether the component corresponds to an element information item from the same schema document or is imported
(References to schema components across namespaces (§5.2.2)) from an external schema (which may,
but need not, correspond to an explicit schema document). The form
of all such references is a
QName. In each of the XML
representation expositions in the following sections, an attribute is shown as
having type QName if and only if it is
interpreted as referencing a schema component.
| Example |
<xs:schema xmlns:xs="http://www.w3.org/1999/XMLSchema"
xmlns:xhtml="http://www.w3.org/1999/html"
xmlns="http://www.foo.com"
targetNamespace="http://www.foo.com">
. . .
<xs:element name="elem1" type="Address"/>
<xs:element name="elem2" type="xhtml:blockquote"/>
<xs:attribute name="attr1"
type="xsl:quantity"/>
. . .
</xs:schema>
|
|
| The first of these is most probably a local reference, i.e. a reference
to a type
definition corresponding to a complexType element information item
located elsewhere in the schema document, the other two refer to type
definitions from schemas for other namespaces and assume that their namespaces
have been declared for import. See References to schema components across namespaces (§5.2.2) for a discussion of importing. |
|
Schema Representation Constraint: QName Interpretation
Where the type of an attribute information item in a schema document is
identified below as
QName, its value is uniformly
interpreted as consisting of a
[Definition:] local name consisting of the character information items after the colon, if any, otherwise all the character information items, in the value, and of a
[Definition:] namespace URI, derived from its value and the containing element information item's [in-scope namespaces] as follows:
- If the value contains a colon, then the [namespace URI] of the member of the [in-scope namespaces] whose [prefix] matches the character information items before the colon. It is an error if no such member is present;
- otherwise (i.e. the value contains no colon)
In the absence of the non-core properties
[in-scope namespaces] and/or
[namespace URI] from the infoset for the schema document in question, processors must reconstruct equivalent information as necessary, using the
[declared namespaces] of the containing element information item and its ancestors in the first case and using the namespace declaration in question's
[children] in the second.
Ed. Note:
If the XML Base proposal is adopted before we go to REC, we will
need to account for any changes it makes to the Infoset in this area.
Schema Representation Constraint: QName resolution
A string known to be a
QName
resolves to a schema component of a specified kind if:
| 1.1 |
that component is contained in the schema which corresponds to the schema
document within which the QName
appears (see Schema Composition (§5.2.2) for a definition of what a schema contains);
|
| 1.2 |
its {local name} matches the local
name of the string;
|
| 1.3 |
its {namespace URI} is identical to the namespace URI of the string.
|
4.3.1 References to Schema Components from Elsewhere
The names of schema components such as type definitions and element
declarations are not of type ID: they are not
unique within a schema, just within a symbol space. This means that simple
fragment identifiers will not work to reference schema components from outside
the context of schema documents.
In the long run we expect to provide some mechanism suitable for referencing
schema components as such. In the mean time, we observe that
[XPointer] provides a mechanism which maps well onto our
notion of symbol spaces as it is reflected in the XML representation of schema components. A fragment identifier of the form
#xpointer(schema/element[@name="person"]) will uniquely identify
the representation of a global element declaration with name person, and similar fragment
identifiers can obviously be constructed for the other global symbol spaces.
Short-form fragment identifiers may also be used in some cases, that is
when a DTD or XML Schema is available for the schema in question, and the
provision of an id attribute for the representations of all primary and secondary schema
components, which is of type
ID, has been exploited.
It is a matter for applications to specify whether they interpret
document-level references of either of the above varieties as being to the relevant element information item (i.e. without
special recognition of the relation of schema documents to schema components) or as being to the
corresponding schema component.
4.4 XML Representation of Schema Components
For each kind of schema component there is a corresponding normative XML representation.
The sections below describe the correspondences between the properties of each kind of
schema component on the one hand and the properties of information items in
that XML representation on the other, together
with constraints on that representation above and beyond those implicit in the
(normative) Schema for Schemas (§A) and (normative) DTD for Schemas (§B).
The language used is as if the correspondences were mappings from XML representation to
schema component, but the mapping in the other direction, and therefor the
correspondence in the abstract, can always be
constructed therefrom.
4.4.1 XML Representation of Attribute Declaration Schema Components
The XML representation for an attribute declaration schema component is an
attribute element information item. It specifies a simple type
definition for an attribute either by reference or explicitly, and may provide
occurrence and default information. The correspondences between the
properties of the information item and
properties of the component are as follows:
XML Representation Summary:
attribute Element Information Item |
|
<attribute
default = string
fixed = string
id = ID
maxOccurs = 0 | 1 : 1
minOccurs = 0 | 1 : 0
name = NCName
type = QName>
Content: (annotation? , simpleType?)
</attribute>
|
If minOccurs=maxOccurs=0 the item
corresponds to no component at all, otherwise |
| Attribute Declaration Schema Component |
| Property | Representation |
| {name} | The value of the name [attribute] |
| {target namespace} | The value of the
targetNamespace [attribute] of the parent schema
element information item, or null if there is none. |
| {simple type definition} | The simple type definition
corresponding to the simpleType element information item in the
[children], if present, otherwise the simple type definition resolved to by
the value of the type [attribute], if present, otherwise the
ur-type definition. |
| {min occurs} | The value of the minOccurs
[attribute], or 0 if it is absent. |
| {max occurs} | The value of the maxOccurs
[attribute], or 1 if it is absent. |
| {value constraint} | If there is a default or a fixed
[attribute], then a pair consisting of the value of that [attribute] and
either default or fixed, as appropriate, otherwise null. |
| {annotation} | The annotation corresponding to the annotation element information item in the
[children], if present, otherwise null. |
|
|
| Example |
<attribute name="myAttribute"/>
<attribute name="yetAnotherAttribute" type="integer" minOccurs="1"/>
<attribute name="anotherAttribute" default="42">
<simpleType basetype="integer">
<minExclusive value="0"/>
</simpleType>
</attribute>
<attribute name="stillAnotherAttribute" type="string" fixed="Hello world!"/>
|
|
Four attributes are declared: one with no explicit
constraints at all; two more each declared by reference to the
built-in simple datatype integer, one required to
be present instances and one with a default and a subrange qualification; and a fourth with a fixed value. |
|
The type attribute is used when the attribute can use a
built-in or pre-declared simple type definition. Otherwise an
anonymous simpleType is used inline.
The default when no simple type definition is referenced or
provided is the ur-type definition, which imposes no constraints at all.
Schema Representation Constraint: Attribute Declaration Representation OK
In addition to the conditions imposed on
attribute element
information items by the DTD and schema for schemas, the following must also hold:
| 1.1 |
default and fixed must not both be present;
|
| 1.2 |
type and simpleType must not both be present;
|
| 1.3 |
The corresponding attribute declaration must satisfy the conditions set
out in Attribute Declaration Constraints (§6.3.1).
|
4.4.2 XML Representation of Element Declaration Schema Components
The XML representation for an element declaration schema component is an
element element information item. It specifies a type
definition for an element either by reference or explicitly, and may provide
occurrence and default information. The correspondences between the
properties of the information item and
properties of the component(s) it corresponds to are as follows:
XML Representation Summary:
element Element Information Item |
|
<element
abstract = boolean : false
block = #all or (possibly empty) subset of {equivClass,
extension, list, restriction, reproduction} : ''
default = string
equivClass = QName
final = #all or (possibly empty) subset of {extension,
restriction, reproduction} : ''
fixed = string
id = ID
maxOccurs = string
minOccurs = non-negative-integer : 1
name = NCName
nullable = boolean : false
ref = QName
type = QName>
Content: (annotation? , (simpleType | complexType)? , (unique | key | keyref)*)
</element>
|
|
If the element element information item has schema as its parent, the corresponding schema component is as follows:
|
| Element Declaration Schema Component |
| Property | Representation |
| {name} | The value of the name [attribute] |
| {target namespace} | The value of the
targetNamespace [attribute] of the parent schema
element information item, or null if there is none. |
| {scope} | global |
| {type definition} | The type definition
corresponding to the simpleType or complexType element information item in the
[children], if either is present, otherwise the type definition resolved to by
the value of the type [attribute], otherwise the {type definition} of the element declaration resolved to by the value of the equivClass [attribute], if present, otherwise the
ur-type definition. |
| {nullable} | The value of the nullable
[attribute], if present, otherwise false. |
| {value constraint} | If there is a default or a fixed
[attribute], then a pair consisting of the value of that [attribute] and
either default or fixed, as appropriate, otherwise null. |
| {identity-constraint definitions} | A set consisting of the
identity-constraint-definitions corresponding to all the key, unique and keyref element information items in the
[children], if any, otherwise the empty set |
| {equivalence class affiliation} | the element declaration resolved to by the
value of the
equivClass [attribute], if present, otherwise null |
| {disallowed substitutions} | A set corresponding to the normalised value of the
block [attribute], if present, otherwise on the value of the
blockDefault [attribute] of the parent schema element
information item, if present, otherwise on the empty string, as follows:
-
the empty string
-
the empty set;
-
#all
-
{equivClass, extension, list,
restriction, reproduction};
-
otherwise
-
a set with members drawn from the set above, each being present or
absent depending on whether the string contains an equivalently named
whitespace-delimited substring.
|
| {equivalence class exclusions} | As for {disallowed substitutions} above, but with the
relevant set being {extension, restriction, reproduction} |
| {abstract} | The value of the abstract
[attribute], if present, otherwise false |
| {annotation} | The annotation corresponding to the annotation element information item in the
[children], if present, otherwise null |
|
|
|
otherwise if the element element information item has
complexType or group as an ancestor and the
ref [attribute] is present, the corresponding schema component is as
follows (unless minOccurs=maxOccurs=0, in which case the item
corresponds to no component at all):
|
|
|
|
otherwise (the element element information item has complexType or group as an ancestor and the ref [attribute] is absent), the corresponding schema components are as follows (unless minOccurs=maxOccurs=0, in which case the item
corresponds to no component at all):
|
|
|
|
|
element corresponds to an element declaration, and allows
the type definition of that declaration to be specified either by reference or
by explicit inclusion.
elements within schema produce
global element declarations; elements within group or complexType produce either particles which contain global element declarations (if there's a ref attribute) or local declarations (otherwise).
Locally-scoped declarations always schema-validate element information items
with a null [namespace URI], regardless of the {target namespace} of the complex type definition they are contained within.
As noted above the names for global are in a separate
symbol space from the symbol spaces for
the names of type definitions, so there can (but need
not be) a simple or complex type definition type with the same name as a
top-level element. As with attribute names, the names of locally-scoped
element declarations reside in symbol spaces local to the type definition which contains
them. Note however that type definition names are always top-level names within a
schema, even when they appear in locally-scoped element declarations.
Note that the above allows for two levels of defaulting for unspecified
type definitions. An element with no referenced or included type definition will
correspond to an element declaration which has the same type definition as the exemplar of its equivalence class if it
identifies one, otherwise the ur-type definition.
See below at XML Representation of Identity-constraint Definition Schema Components (§4.4.8) for key, unique and keyref.
| Example |
<xs:element name="myelement" type="mySimpleType"/>
<xs:element name="et0" type="myComplexType"/>
<xs:element name="et1">
<xs:complexType>
<xs:element ref="et0"/>
. . .
<xs:attribute ...>. . .</xs:attribute>
</xs:complexType>
</xs:element>
<xs:element name="et2">
<xs:complexType content="empty">
<xs:attribute ...>. . .</xs:attribute>
</xs:complexType>
</xs:element>
|
|
| The first two examples above declare elements by reference to a simple and a
complex type definition respectively. The third and fourth use embedded anonymous complex
type definitions, the first of which in
turn refers to one of the top-level element declarations in its content model. |
<xs:element name="contextOne">
<xs:complexType>
<xs:element name="myLocalelement" type="myFirstType"/>
<xs:element ref="globalelement"/>
</xs:complexType>
</xs:element>
<xs:element name="contextTwo">
<xs:complexType>
<xs:element name="myLocalelement" type="mySecondType"/>
<xs:element ref="globalelement"/>
</xs:complexType>
</xs:element>
|
|
Instances of myLocalelement within
contextOne will be constrained by myFirstType,
while those within contextTwo will be constrained by
mySecondType. |
|
NOTE:
The possibility that differing attribute declarations and/or content models
would apply to elements with the same name in different contexts is an
extension beyond the expressive power of a DTD in XML 1.0.
| Example |
<xs:complexType name="facet" base="annotated" derivedBy="extension">
<xs:attribute name="value" minOccurs="1"/>
</xs:complexType>
<xs:element name="facet" type="facet" abstract="true"/>
<xs:element name="encoding" equivClass="facet">
<xs:complexType base="facet" derivedBy="restriction">
<xs:attribute name="value" type="encodings"/>
</xs:complexType>
</xs:element>
<xs:element name="period" equivClass="facet">
<xs:complexType base="facet" derivedBy="restriction">
<xs:attribute name="value" type="timeDuration"/>
</xs:complexType>
</xs:element>
<xs:complexType name="datatype">
<xs:element ref="facet" minOccurs="0" maxOccurs="*"/>
<xs:attribute name="name" type="NCName" minOccurs="0">
. . .
</xs:complexType>
|
|
An example from the schema for datatypes from [XML Schemas: Datatypes]. The
facet type is defined
and the facet element is declared to use it. The facet element is abstract -- it's
only defined to stand as the exemplar for a class. Two further
elements are declared, each a member of the facet equivalence
class. Finally a type is defined which refers to facet, thereby
allowing either period or encoding (or
any other member of the class). |
|
Schema Representation Constraint: Element Declaration Representation OK
In addition to the conditions imposed on
element element
information items by the DTD and schema for schemas, the following must also hold:
| 1.1 |
default and fixed must not both be present;
|
| 1.2 |
If the element's parent is schema, then
| 1.2.1.1 |
name must be present;
|
| 1.2.1.2 |
minOccurs, maxOccurs and ref must be absent;
|
otherwise
| 1.2.2.1 |
One of ref or name must be present, but not both;
|
| 1.2.2.2 |
equivClass and final must be absent;
|
| 1.2.2.3 |
If ref is present, then all of complexType,
simpleType, type, key,
unique and keyref must be absent;
|
|
| 1.3 |
type and either simpleType or complexType are mutually exclusive;
|
| 1.4 |
The corresponding particle and/or element declarations must satisfy the conditions set
out in Element Declaration Constraints (§6.3.2) and Particle Constraints (§6.3.10).
|
4.4.3 XML Representation of Complex Type Definition Schema Components
The XML representation for a complex type definition schema component is a
complexType element information item. It provides validation
information for the [attributes] and [children] of an element information
item in the form of attribute declarations and a content type. The correspondences between the
properties of the information item and
properties of the component(s) it corresponds to are as follows:
XML Representation Summary:
complexType Element Information Item |
|
<complexType
abstract = boolean : false
base = QName
block = #all or (possibly empty) subset of {extension,
restriction, reproduction}
content = elementOnly | empty | mixed | textOnly
derivedBy = extension | restriction | reproduction
final = #all or (possibly empty) subset of {extension,
restriction, reproduction}
id = ID
name = NCName>
Content: (annotation? , (((minBound | minExclusive | minInclusive | maxBound | maxExclusive | maxInclusive | precision | scale | length | minlength | maxlength | encoding | period | enumeration | pattern)* | ((element | group | all | choice | sequence | any))*) , (((attribute | attributeGroup)* , anyAttribute?))))
</complexType>
|
|
<attributeGroup
id = ID
name = NCName
ref = QName>
Content: (annotation? , (attribute | attributeGroup)* , anyAttribute?)
</attributeGroup>
|
|
<anyAttribute
namespace = ##any | ##other | ##local | list of {uri, ##targetNamespace} : ##any
/>
|
| Complex Type Definition Schema Component |
| Property | Representation |
| {name} | The value of the name [attribute] if present, otherwise null |
| {target namespace} | The value of the
targetNamespace [attribute] of the schema ancestor
element information item if present, otherwise null |
| {base type definition} | The type definition resolved to by the
value of the base [attribute], if present, otherwise the simple
ur-type definition if the
content [attribute] is textOnly, otherwise the complex ur-type definition |
| {derivation method} | If the derivedBy [attribute]
is present, the member of the set {extension, restriction, reproduction} corresponding to its value, otherwise if there are any
[children] other than annotation then restriction, otherwise reproduction |
| {abstract} | The value of the abstract
[attribute], if present, otherwise false |
| {attribute declarations} | The union of the set of attribute
declarations corresponding to the attribute [children] of the
item, if any, with the {attribute declarations} of the
attribute groups resolved to by the values of the ref
[attribute] of the attributeGroup [children], if any. In
the latter case, if the {target namespace} of any referenced
group is not identical to the {target namespace} of this
type definition, the attribute declarations are not the attribute declarations
from the corresponding {attribute declarations} as such, but
distinct attribute declarations sharing all properties with them except for
{target namespace}, which has the value of {target namespace}s from their original containing group. |
| {attribute wildcard} |
-
If there are no attributeGroup [children] corresponding to attribute groups with non-null {attribute wildcard}s, a value depending on the string value of the
namespace [attribute] of the anyAttribute if there is one as follows:
-
##any
-
any
-
##other
-
a pair of not and the value of the
targetNamespace [attribute] of the schema ancestor
element information item if present, otherwise null
-
otherwise
-
a set whose members are namespace URIs corresponding to the
whitespace-delimited substrings of the string, except
-
if one such
substring is
##targetNamespace, the corresponding member is the value of the targetNamespace [attribute] of the schema ancestor
element information item if present, otherwise null
-
if one such
substring is
##local, the corresponding member is null
otherwise null.
-
Otherwise the intensional intersection of a value as defined in (1) above
and all the non-null {attribute wildcard}s of the attribute groups corresponding to the attributeGroup [children], as defined in Attribute Wildcard Intersection (§6.3.4).
|
| {content type} |
- If the
content [attribute] is empty,
then empty;
- otherwise if the
base [attribute] is present and
either the type definition resolved to by the
value of the base [attribute] is a simple type definition, or it
is a complex type definition whose own {content type} is a
simple type definition, then
a simple type definition which restricts that simple type definition with the
facets corresponding to the minBound, minExclusive, minInclusive,
maxBound, maxExclusive, maxInclusive, precision, scale, length, minlength, maxlength, encoding, period, enumeration and pattern [children], if any, as
defined in Simple Type Restriction (Facets) (§4.4.11).
-
otherwise if the
content [attribute] is
elementOnly or mixed, a pair of that value and a particle
as follows:
[Definition:] Let the explicit particle be as follows:
-
If there is exactly one all, choice or
sequence among the [children] and no any,
group or element [children], then the particle corresponding to that all, choice or
sequence;
-
otherwise if the
content [attribute] is
elementOnly then a particle whose properties are as follows:
-
{min occurs}
-
1
-
{max occurs}
-
1
-
{term}
-
A model group whose {compositor} is
sequence and whose {particles} is the sequence of particles
corresponding to all the all, choice,
sequence, any,
group or element items among the [children],
in order.
-
otherwise if the
content [attribute] is
mixed then a particle whose properties are as follows:
-
{min occurs}
-
0
-
{max occurs}
-
*
-
{term}
-
A model group whose {compositor} is
choice and whose {particles} are as above for the
elementOnly case.
The actual value then depends on the derivedBy
[attribute] as follows:
-
If it is restriction or reproduction, then the explicit
particle itself;
-
If it is extension, then if the type definition resolved to
by the value of the
base [attribute] has a {content type} of empty, the explicit
particle itself, otherwise a particle whose properties are as follows:
-
{min occurs}
-
1
-
{max occurs}
-
1
-
{term}
-
A model group whose {compositor} is
sequence and whose {particles} are the particle of the
the {content type} of the type definition resolved to
by the value of the
base [attribute] followed by the explicit
particle.
-
If it is absent, then the explicit
particle itself (this can only happen if the
base is the ur-type).
- otherwise (the
content [attribute] is
textonly but there is no base [attribute]) the simple
ur-type definition
|
| {prohibited-substitutions} | A set corresponding to the normalised value of the
block [attribute], if present, otherwise on the value of the
blockDefault [attribute] of the parent schema element
information item, if present, otherwise on the empty string, as follows:
-
the empty string
-
the empty set;
-
#all
-
{extension, restriction, reproduction};
-
otherwise
-
a set with members drawn from the set above, each being present or
absent depending on whether the string contains an equivalently named
whitespace-delimited substring.
NOTE:
Although the blockDefault [attribute] of schema may include the values equivClass and list, these values are ignored in the determination of {prohibited-substitutions} for type definitions (it is used in the determination of {disallowed substitutions} for element declarations)
|
| {final} | As for {prohibited-substitutions} above |
| {annotation} | The annotation corresponding to the annotation element information item in the
[children], if present, otherwise null |
|
|
Ed. Note:
base requires derivedBy; attrs unique; facets requires base
[Unrestructured material elided]
4.4.4 XML Representation of Attribute Group Definition Schema Components
The XML representation for an attribute group definition schema component is an
attributeGroup element information item. It provides for
naming a group of attribute declarations and an attribute wildcard for use in
complex type definitions and other attribute group definitions. The correspondences between the
properties of the information item and
properties of the component it corresponds to are as follows:
[Unrestructured material elided]
4.4.5 XML Representation of Model Group Definition Schema Components
This reconstructs another common use of parameter entities.
[Unrestructured material elided]
4.4.6 XML Representation of Model Group Schema Components
[Unrestructured material elided]
4.4.7 XML Representation of Wildcard Schema Components
In order to exploit the full potential for extensibility offered by XML
plus namespaces, more provision is needed than DTDs allow for targeted flexibility in content
models and attribute declarations. At a given point in a content model, in
addition to what DTDs provide for we need particles that allow the following:
-
Any well-formed XML element item: any tag, any namespace, any attributes,
any content, as long as it's well-formed;
-
Any well-formed XML element item, provided it's in some other
namespace than the one we're defining a type for;
-
Any well-formed XML element item, provided it's in a specified namespace;
-
Any well-formed XML element item, provided it's from the same
namespace as the one we're defining a type for.
Of course, by qualifying one of these with a *, we allow for any
amount of (localised) flexibility in validation.
Attributes need the same kind of flexibility: a good-citizen schema
should probably allow any attributes from the xml: namespace, for instance.
XML Representation Summary:
any Element Information Item |
|
<any
maxOccurs = string
minOccurs = non-negative-integer : 1
namespace = ##any | ##other | ##local | list of {uri, ##targetNamespace} : ##any
processContents = lax | skip | strict : strict
/>
|
|
|
Ed. Note:
The above not complete yet -- processContents needs to be added to
the wildcard component, and the correspondences above filled in.
The four alternatives for the namespace attribute
correspond to the four kinds of flexibility listed above.
[Unrestructured material elided]
4.4.8 XML Representation of Identity-constraint Definition Schema Components
We supplement the simple uniqueness and reference mechanisms provided by
ID and IDREF in XML 1.0 and SGML with three new kinds
of constraint, for uniqueness, keys and key references.
Ed. Note:
Not complete, above property correspondences need to be filled in.
The XPathExprApprox simple type referenced above
is defined in (normative) Schema for Schemas (§A). It is a
permissive approximation to the syntax of XPath expressions as defined
in [XPath], and is not an accurate
reconstruction of that syntax. Its use by reference from other schema
documents is deprecated: In due course a schema for XPath
will be published which includes a simple type definition appropriate
for widespread use.
[Unrestructured material elided]
4.4.9 XML Representation of Notation Declaration Schema Components
A notation may be declared by specifying a name and an identifier for the
notation.
Ed. Note:
Not complete, above property correspondences need to be filled in.
| Example |
<notation name="jpeg"
public="image/jpeg" system="viewer.exe" />
<element name="picture">
<type base="binary" derivedBy="extension">
<attribute name="pictype" type="NOTATION"/>
</type>
</element>
<picture pictype="jpeg">...</picture>
|
|
|
4.4.10 XML Representation of Annotation Schema Components
Annotation of schemas and schema components, with material for human or
computer consumption, is provided for by allowing application information and
human information at the beginning of most major schema elements, and anywhere
at the top level of schemas.
XML Representation Summary:
annotation Element Information Item |
|
<annotation>
Content: (appinfo | documentation)*
</annotation>
|
|
|
Ed. Note:
Not complete, above property correspondences need to be filled in.
{user information} is intended for human consumption, {application information} for automatic processing. In both cases, provision is made for an optional URI reference to supplement the local information. Schema validation does not involve dereferencing these URIs, when present. In the case of {user information}, indication may be given as to the identity of the (human) language used in the contents, using the xml:lang attribute.
4.4.11 XML Representation of Simple Type Definition Schema Components
See [XML Schemas: Datatypes]
[Unrestructured material elided]
Schema Representation Constraint: Simple Type Restriction (Facets)
A simple type definition restricts another simple type definition with a
set of facets if: watch this space.
5 Schema Access and Composition
This chapter defines the mechanisms by which we establish the necessary precondition for establishing schema-validity, namely access to one or more schemas. This chapter also describes in detail related mechanisms for using in
one schema, definitions and declarations from another.
Chapter 6 provides a formal definition of schema-validation. Here we set out
in detail the 3-layer architecture implied by the preceding chapters which
prepares for that formal definition and relates it
to XML documents and WWW-situated processes. This layering is provided to
maximise the range of environments in which this specification can be applied,
and to minimise the need for modifications to this specification as new
standards and conventions for Web interoperability are developed. The layers
are:
- The schema-validation core, relating schema components and instance
information items;
- Schema representation: the connections between XML
representations and schema components, including the
relationships between namespaces and schema components;
- XML Schema web-interoperability guidelines: instance->schema and
schema->schema connections for the WWW.
Layer 1 specifies the manner in which a schema composed of schema components
can be applied to validate an instance element information item. Layer 2, which is
primarily defined in Chapter 4, specifies the use of schema
elements in XML documents as the standard XML representation for
schema information in a broad range of computer systems and execution
environments. To support interoperation over the World Wide Web in particular,
layer 3 provides a set of conventions for schema reference on the
Web.
We note that improved or alternative conventions for Web interoperability can
be standardised in the future without reopening this recommendation. For
example, the W3C is currently considering initiatives to standardise the
packaging of resources relating to particular documents and/or namespaces: this
would be an addition to the mechanisms described here for layer 3. This
architecture also facilitates innovation at layer 2: for example, it would be
possible in the future to define an additional standard for the representation of
schema components which allowed e.g. type definitions to be specified piece by
piece, rather than all at once.
5.1 Layer 1: Summary of the schema-validation core
The fundamental purpose of the schema-validation core is to define schema-validatity for a single
element information item and its descendants with respect to a specified
complex type
definition. All processors are required to implement this core predicate in a
manner which conforms exactly to this specification.
Schema-validity is defined with reference to schema (note not a
schema document) which consists of (at a minimum) the set of schema
components (definitions and declarations) required for that
validation. This is not a circular definition, but rather a
post facto observation: no element information item can
be schema-valid unless all the components required by any aspect of
its (potentially recursive) validation are present in the schema.
As specified above, each schema component is associated directly or
indirectly with a target namespace, or explicitly with no namespace. In the case of multi-namespace documents,
components for more than one target namespace will co-exist in the
complete component
set.
Processors have the option to assemble ( and perhaps to optimise or pre-compile) the entire schema prior to the start of a validation episode, or to
gather the schema lazily as individual components are required. In all
cases it is required that:
- The processor succeed in locating the definitions and declarations
transitively required to complete a validation;
- that no definition or declaration changes once it has been located;
- If the processor chooses to acquire declarations and definitions
dynamically, that there be no side effects of such dynamic acquisition that
would cause the results of validation to differ from that which would have
been obtained from the same schema components acquired in bulk.
NOTE: the validation core is defined in terms of the schema components
comprising a complete component set; no mention is made of the schema definition
syntax (i.e. schema). Although many processors will acquire
schemas in this format, others may operate on compiled representations, on a
programmatic representation as exposed in some programming language, etc.
[Definition:] The fundamental schema-valid predicate
applies to an element information item (EII) and
a complex type definition against the background of a schema.
Ed. Note:
We need to add more to this now that we've allowed partial processing
under <any/>
The obligation of a schema-aware processor as far as the schema-validation
core is concerned is to implement the definition of schema-valid. The
choice of EII, as well as the determination of the complex type
definition and schema is not specified at layer 1.
The schema-valid predicate is defined recursively, and e.g. streaming
processors may implement it in a way that augments the schema during
processing in response to encountering new namespaces. The implication of the
invariants expressed above is that schema-valid must be implemented so
that the same validation outcome is given in such cases as would be given if the initial invocation of
schema-valid was re-performed
with the final schema replacing the one initially employed.
5.2 Layer 2: Schema definitions in XML
This is described in XML Representation of Schemas and Schema Components (§4), which defines an
XML representation for type definitions and element declarations and so on,
specifying their target namespace and collecting them into schema documents.
NOTE: The two following sections relate to assembling the complete component set for validation from multiple sources. They should not be understood as a form of text substitution, but rather as providing mechanisms for distributed definition of schema components, with appropriate schema-specific semantics.
Ed. Note: "schemaLocation" really belongs at layer 3 . . .
5.2.1 Assembling a schema for a single namespace from multiple schema definition documents
[Unrestructured material elided]
5.2.2 References to schema components across namespaces
As described in XML Schema Abstract Data Model (§2.2), every global schema component is associated with
a target namespace (or, explicitly, with none). In this section we set out
the exact mechanism and syntax in the XML form of
schema definition by which a reference to a foreign component is made, that is, a component with a different target namespace from that of the referring component.
We require not only a means
of addressing such foreign components but also a signal to schema-aware processors that a
schema document contains such preferences and differentiates two subtly
different cases:
[Unrestructured material elided]
Schema Representation Constraint: Schema Composition
The schema which corresponds to a schema document (that is, a
schema element information item) contains all the primary
and secondary schema components which correspond to the immediate element
information item
[children] of that schema document, together with any
primary or secondary components which are:
| 1.1 |
contained in a schema identified by an include element
information item from among the [children] of that schema document;
|
or
| 1.2 |
contained in a schema identified by an import element
information item from among the [children] of that schema document;
|
[Unrestructured material elided]
5.3 Layer 3: Web-interoperability
Layers 1 and 2 provide a framework for validation and XML definition of schemas in a broad variety of environments. Over time, we expect that a range
of standards and conventions will evolve to support interoperability of XML
Schema implementations on the World Wide Web. Layer 3 defines the minimum level
of function required of all conformant processors operating on the Web:
it is intended that, over time, future standards (e.g. XML Packages) for interoperability on the
Web and in other environments can be introduced without the need to republish
this specification.
NOTE: The core validation architecture requires that the complete
component set of
appropriate declarations for each global element and attribute be
available. This requires may involve both resolving both
instance->schema and schema->schema references. As observed above, we anticipate
that the precise mechanisms for resolving such references will evolve over time.
In support of such evolution, we have attempted to observe the design principle that references from
one schema to another use mechanisms that directly parallel those used to
reference a schema from an instance document.
5.3.1 Standards for representation and retrieval of schema definitions on the Web
For interoperability, schema definitions like all other Web resources are identified by
URI and retrieved using the standard mechanisms of the Web (e.g. http, https,
etc.) Schema definitions on the Web must be part of documents with the mime type text/xml, and are represented in the
standard XML schema definition form described by layer two (I.e. as <schema>
elements).
NOTE: there will often be times when a schema definition will be a
complete XML 1.0 document with a root element of <schema>. There will be
other occasions in which <schema> elements will be contained in other
documents, perhaps referenced using fragment and/or Xpointer notation.
5.3.2 How schema definitions are located on the Web
As described in Layer 1: Summary of the schema-validation core (§5.1), processors are responsible for providing the
schema components (definitions and declarations) needed for validation. This
section introduces a set of normative conventions to facilitate interoperability
for instance documents and schemas retrieved and validated from the Web.
NOTE: As discussed above in Layer 2: Schema definitions in XML (§5.2), other non-Web mechanisms for delivering schemas for validation may exist, but are outside the scope of this recommendation.
The validation mechanisms of Layer 1: Summary of the schema-validation core (§5.1) specify that schema-valid
applies to an element information item to be validated, and the type
to be used to
validate it. Documents on the Web can be validated in their entirety, from the
document root element, or else individual elements can be selectively validated.
Processors on the Web are free to attempt validation against arbitrary
complete component sets (as defined in Layer 1: Summary of the schema-validation core (§5.1)) and against any type. However, it
is useful to have a common convention for determining a complete component set, and
an initial type. For this purpose, we require that for general-purpose schema-aware processors (i.e. those not specialised to one or a fixed set of pre-determined schemas), unless directed otherwise by a user the element information
item to be validated is either the document element of an information
set, or the local root of a new namespace-governed region within an
information set.
To determine the type declaration to be used for the validation in these cases, the
processor is required to retrieve a schema document with a "targetNamespace"
identical to the
namespace URI, if any, of the element information item to be
validated. Again, unless directed otherwise, the processor must
locate within that schema a global element declaration with an NCName matching
that of the element information item to be validated. The processor must ensure that both the
element declaration, and the type declaration used in that element declaration,
are included in the complete component set for the validation. The type thus
identified is the type used for validation of the element information item. The composition of the complete component set for validation is governed by Layer 2: Schema definitions in XML (§5.2) above.
The means used to locate appropriate schema document(s) are processor and
application dependent, subject to a following requirements:
- Schemas are represented on the Web in the form specified by Chapter 3.
- The author of a document uses namespace declarations to indicate the intended
interpretation of names appearing therein; there may not be a schema
retrievable via the namespace URI. Processors should not attempt to dereference namespace URIs unless explicitly directed to do so.
NOTE: Experience suggests that it is not in general safe or desirable from
a performance point of view to dereference NS URIs as a matter of course. User community and/or consumer/provider agreements may establish conventions which make this a sensible strategy: This recommendation allows but does not require this. Users are always free to supply namespace URIs as schema location information when dereferencing is desired: see below.
-
On the other hand, in case a document author (human or not) created a
document with a particular schema in view, and warrents that some or
all of the document is schema-valid per that schema, we provide the
"schemaLocation" attribute (in the XML Schema namespace) to record
this fact with pairs of URI references (one for the namespace URI, and
one for the schema definition).
Again, unless directed otherwise general-purpose schema-aware processors must attempt to dereference each schema URI in the
value of "schemaLocation" to obtain a schema, whose target namespace
must be identical to the namespace it appears in conjunction with, if any.
Failure to
dereference the URI, failure to locate a valid document of mime type
text/xml, failure to find a <schema> or mismatch of the targetNamespace URI is an error.
-
"schemaLocation" attributes can occur on any element participating in a
validation, and all such attributes must be processed as if they had occurred at the validation root. According to the rules of
Layer 1: Summary of the schema-validation core (§5.1), the complete component set can be lazily assembled, but is otherwise
stable throughout a validation. Although schema location attributes can occur
on any element, and can be processed incrementally as discovered, their effect
is essentially global to the validation. Definitions and declarations remain
in effect beyond the scope of the element on which the binding is declared.
NOTE: The issue of the value space for QNames, in particular in the case of prefixes with no declaration, needs to be carefully elucidated in the Datatype draft.
Multiple schema bindings can be declared using a single
attribute. For example consider a stylesheet:
<stylesheet xmlns="http://www.w3.org/1999/Style/Transform"
xmlns:html="http://www.w3.org/1999/XHTML"
xmlns:xsi="http://www.w3.org/1999/XMLSchema/instance"
xsi:schemaLocation="http://www.w3.org/1999/Style/Transform
http://www.w3.org/1999/Style/Transform/xslt.xsd
http://www.w3.org/1999/XHTML
http://www.w3.org/1999/XHTML/xhtml.xsd"
NOTE: the namespace URIs used in "schemaLocation" can, but need not
be identical to those actually qualifying the element within whose start tag it is found or its other attributes. For example, all
schema location information can be declared on the document element
of a document, if desired,
regardless of where the namespaces are actually used.
Ed. Note: Need to worry about the 'no namespace' case -- what do I put in "schemaLocation" if I don't declare _any_ namespaces?
Ed. Note: We've left ourselves with no way in a component which _does_ have a target namespace to refer to a component with none.
A (normative) Schema for Schemas
The XML Schema definition for XML Schema: Structures itself is presented here as normative
part of the specification, and as an illustrative example of the XML Schema in
defining itself with the very constructs that it defines. The names of XML
Schema language types, elements, attributes and groups defined here
are evocative of their purpose, but are occasionally verbose.
There is some annotation in comments, but a fuller annotation will require
the use of embedded documentation facilities or a hyperlinked external
annotation for which tools are not yet readily available.
Since an XML Schema: Structures is an XML document, it has optional XML and doctype
declarations that are provided here for completeness. The root
schema element defines a new schema. Since this is a schema for
XML Schema: Structures, the targetNamespace references the XML Schema namespace itself.
<?xml version='1.0'?>
<!-- XML Schema schema for XML Schemas: Part 1: Structures -->
<!-- Note this schema is NOT the normative structures schema - - the
prose copy in the structures REC is the normative version (which
shouldn't differ from this one except for this comment and entity
expansions, but just in case -->
<!DOCTYPE schema PUBLIC "-//W3C//DTD XMLSCHEMA 19991216//EN" "structures.dtd" >
<schema xmlns="&XMLSchemaNS;" targetNamespace="&XMLSchemaNS;" blockDefault="#all" version="$Id: structures.html,v 1.2 2000/02/25 17:46:33 connolly Exp $">
<!-- The datatype element and all of its members are defined
in XML Schema: Part 2: Datatypes -->
<include schemaLocation="&XSP2.URI;.xsd"/>
<element name="schemaTop" abstract="true" type="annotated">
<annotation>
<documentation>This abstract element defines an equivalence class over the
elements which occur freely at the top level of schemas.
These are: datatype, type, element, attributeGroup, group, notation
All of their types are based on the "annotated" type
by extension.</documentation>
</annotation>
</element>
<!-- schema element -->
<element name="schema">
<complexType base="openAttrs" derivedBy="extension" content='elementOnly'>
<sequence>
<choice minOccurs="0" maxOccurs="*">
<element ref="include"/>
<element ref="import"/>
<element ref="annotation"/>
</choice>
<sequence minOccurs="1" maxOccurs="*">
<element ref="schemaTop"/>
<element ref="annotation" minOccurs="0" maxOccurs="*"/>
</sequence>
</sequence>
<attribute name="targetNamespace" type="uri-reference"/>
<attribute name="version" type="string"/>
<attribute name="finalDefault" type="derivationSet" default=""/>
<attribute name="blockDefault" type="blockSet" default=""/>
<attribute name="id" type="ID"/>
</complexType>
<key name="element">
<selector>element</selector>
<field>@name</field>
</key>
<key name="complexType">
<selector>complexType</selector>
<field>@name</field>
</key>
<key name="group">
<selector>group</selector>
<field>@name</field>
</key>
<key name="attributeGroup">
<selector>attributeGroup</selector>
<field>@name</field>
</key>
<key name="notation">
<selector>notation</selector>
<field>@name</field>
</key>
<key name="simpleType">
<selector>simpleType</selector>
<field>@name</field>
</key>
<key name="keyOrUnique">
<selector>.//key|.//unique</selector>
<field>@name</field>
</key>
<key name="constraint">
<selector>.//key|.//unique|.//keyref</selector>
<field>@name</field>
</key>
<key name="keyref">
<selector>.//keyref</selector>
<field>@name</field>
</key>
</element>
<!-- For references to a type -->
<!-- 'element', 'attribute' and any all use this -->
<attributeGroup name="typeRef">
<attribute name="type" type="QName"/>
</attributeGroup>
<!-- For 'element' and 'attribute' -->
<attributeGroup name="valueConstraint">
<attribute name="default" type="string"/>
<attribute name="fixed" type="string"/>
</attributeGroup>
<!-- for all particles -->
<attributeGroup name="occurs">
<attribute name="minOccurs" type="non-negative-integer" default="1"/>
<attribute name="maxOccurs" type="string"/> <!-- allows '*', so integer
won't do -->
</attributeGroup>
<!-- for element, group and attributeGroup, which both define and reference -->
<attributeGroup name="defRef">
<attribute name="name" type="NCName" minOccurs="0"/>
<attribute name="ref" type="QName" minOccurs="0"/>
</attributeGroup>
<!-- 'element', 'group' and 'any' -->
<group name="particle">
<choice>
<element ref="element"/>
<element ref="group"/>
<element ref="all"/>
<element ref="choice"/>
<element ref="sequence"/>
<element ref="any"/>
</choice>
</group>
<element name="sic">
<complexType content="empty"/>
</element>
<group name="attrDecls">
<sequence>
<choice minOccurs="0" maxOccurs="*">
<element ref="attribute"/>
<element ref="attributeGroup"/>
</choice>
<element ref="anyAttribute" minOccurs="0"/>
</sequence>
</group>
<element name="anyAttribute">
<complexType name="anyAttribute" content="empty">
<attribute name="namespace" type="namespaceList" default="##any"/>
</complexType>
</element>
<!-- types for type -->
<complexType name="complexType" base="annotated" derivedBy="extension" abstract="true">
<sequence>
<choice>
<element ref="facet" minOccurs="0" maxOccurs="*"/>
<!-- max 1, min 0, for each facet except pattern, period-->
<group ref="particle" minOccurs="0" maxOccurs="*"/>
</choice>
<group ref="attrDecls"/>
</sequence>
<attribute name="name" type="NCName" minOccurs="0">
<annotation>
<documentation>Will be restricted to required or forbidden</documentation>
</annotation>
</attribute>
<attribute name="content">
<simpleType base="NMTOKEN">
<enumeration value="elementOnly"/>
<enumeration value="textOnly"/>
<enumeration value="mixed"/>
<enumeration value="empty"/>
</simpleType>
</attribute>
<attribute name="base" type="QName"/>
<attribute name="derivedBy" type="derivationChoice"/>
<attribute name="abstract" type="boolean" default="false"/>
<attribute name="final" type="derivationSet"/>
<attribute name="block" type="derivationSet"/>
</complexType>
<complexType name="namedType" base="complexType" derivedBy="restriction">
<annotation>
<documentation>This was for the top-level type element, daughter of <schema</documentation>
</annotation>
<attribute name="name" minOccurs="1">
<annotation><documentation>Required at the top level</documentation></annotation>
</attribute>
</complexType>
<complexType name="anonType" base="complexType" derivedBy="restriction">
<annotation>
<documentation>This was for the nested type element, daughter of <element</documentation>
</annotation>
<attribute name="name" maxOccurs="0">
<annotation><documentation>Forbidden when nested</documentation></annotation>
</attribute>
</complexType>
<!-- Top level type element, daughter of schema -->
<element name="complexType" equivClass="schemaTop" type="complexType"/>
<simpleType name="derivationChoice" base="NMTOKEN">
<annotation>
<documentation>A utility type, not for public use</documentation>
</annotation>
<enumeration value="extension"/>
<enumeration value="restriction"/>
<enumeration value="reproduction"/>
</simpleType>
<simpleType name="blockSet" base="string">
<annotation>
<documentation>#all or (possibly empty) subset of {equivClass,
extension, list, restriction, reproduction}</documentation>
<documentation>A utility type, not for public use</documentation>
<documentation>Should be a sequence drawn from the values of derivationChoice
plus 'equivClass' and 'list'
or #all -- regexp is only an approximation</documentation>
</annotation>
<pattern value="#all?|(equivClass|extension|list|restriction|reproduction| )*"/>
</simpleType>
<simpleType name="derivationSet" base="string">
<annotation>
<documentation>#all or (possibly empty) subset of {extension,
restriction, reproduction}</documentation>
<documentation>A utility type, not for public use</documentation>
<documentation>Should be a sequence drawn from the values of derivationChoice,
or #all -- regexp is only an approximation</documentation>
</annotation>
<pattern value="#all?|(extension|restriction|reproduction| )*"/>
</simpleType>
<!-- The element element can be used either
at the toplevel to define an element-type binding globally,
or within a content model to either reference a globally-defined
element or type or declare an element-type binding locally.
The ref form is not allowed at the top level -->
<complexType name="element" base="annotated" derivedBy="extension">
<choice minOccurs="0">
<element ref="simpleType"/>
<element ref="complexType"/>
</choice>
<element ref="identity-constraint" minOccurs="0" maxOccurs="*"/>
<attributeGroup ref="defRef"/>
<attributeGroup ref="typeRef"/>
<attribute name="equivClass" type="QName"/>
<attributeGroup ref="occurs"/>
<attributeGroup ref="valueConstraint"/>
<attribute name="nullable" type="boolean" default="false"/>
<attribute name="abstract" type="boolean" default="false"/>
<attribute name="final" type="derivationSet" default=""/>
<attribute name="block" type="blockSet" default=""/>
</complexType>
<complexType name="namedElement" base="element" derivedBy="restriction">
<attribute name="name" minOccurs="1"/> <!-- required at top level -->
<attribute name="ref" maxOccurs="0"/> <!-- forbidden at top level -->
</complexType>
<element name="element" type="element" equivClass="schemaTop"/>
<!-- group type for the three kinds of group -->
<complexType name="explicitGroup" base="annotated" derivedBy="extension">
<group ref="particle" minOccurs="0" maxOccurs="*"/>
<attributeGroup ref="occurs"/>
</complexType>
<element name="all" type="explicitGroup"/>
<element name="choice" type="explicitGroup"/>
<element name="sequence" type="explicitGroup"/>
<!-- group type for named top-level groups and group references -->
<complexType name="group" base="explicitGroup" derivedBy="extension" abstract="true">
<attributeGroup ref="defRef"/>
</complexType>
<complexType name="namedGroup" base="group" derivedBy="restriction">
<attribute name="name" minOccurs="1"/> <!-- required at top level -->
<attribute name="ref" maxOccurs="0"/> <!-- forbidden at top level -->
</complexType>
<complexType name="anonGroup" base="group" derivedBy="restriction">
<!-- required at top level -->
<attribute name="name" maxOccurs="0"/> <!-- forbidden when nested -->
</complexType>
<element name="group" equivClass="schemaTop" type="group"/>
<!-- The wildcard specifier in content models -->
<element name="any">
<complexType content="empty" base="openAttrs" derivedBy="extension">
<attribute name="namespace" type="namespaceList" default="##any"/>
<attribute name="processContents" default="strict">
<simpleType base="NMTOKEN">
<enumeration value="skip"/>
<enumeration value="lax"/>
<enumeration value="strict"/>
</simpleType>
</attribute>
<attributeGroup ref="occurs"/>
</complexType>
</element>
<!-- simple type for the value of the 'namespace' attr of 'any' and
'anyAttribute' -->
<!-- Value is
##any - - any non-conflicting WFXML/attribute at all
##other - - any non-conflicting WFXML/attribute from
namespace other than targetNS
##local - - any unqualified non-conflicting WFXML/attribute
one or - - any non-conflicting WFXML/attribute from
more URI the listed namespaces
references
(space separated)
##targetNamespace may appear in the above list, to refer to the
targetNamespace of the enclosing schema -->
<simpleType name="namespaceList" base="string">
<annotation>
<documentation>##any | ##other | ##local | list of {uri, ##targetNamespace}</documentation>
<documentation>A utility type, not for public use</documentation>
</annotation>
</simpleType>
<!-- the attribute element declares attributes -->
<element name="attribute">
<complexType base="annotated" derivedBy="extension">
<element ref="simpleType" minOccurs="0"/>
<attribute name="name" type="NCName" minOccurs="1"/>
<attributeGroup ref="typeRef"/>
<attribute name="minOccurs" default="0">
<simpleType base="non-negative-integer">
<enumeration value="0"/>
<enumeration value="1"/>
</simpleType>
</attribute>
<attribute name="maxOccurs" default="1">
<simpleType base="non-negative-integer">
<enumeration value="0"/>
<enumeration value="1"/>
</simpleType>
</attribute>
<attributeGroup ref="valueConstraint"/>
</complexType>
</element>
<!-- attributeGroup element -->
<complexType name="attributeGroup" base="annotated" derivedBy="extension" abstract="true">
<choice minOccurs="0" maxOccurs="*">
<element ref="attribute"/>
<element ref="attributeGroup"/>
</choice>
<element ref="anyAttribute" minOccurs="0"/>
<attributeGroup ref="defRef"/>
</complexType>
<complexType name="namedAttributeGroup" base="attributeGroup" derivedBy="restriction">
<attribute name="name" minOccurs="1"/> <!-- required at top level -->
<attribute name="ref" maxOccurs="0"/> <!-- forbidden at top level -->
</complexType>
<complexType name="anonAttributeGroup" base="attributeGroup" derivedBy="restriction">
<attribute name="ref" minOccurs="1"/> <!-- required when nested -->
<attribute name="name" maxOccurs="0"/> <!-- forbidden when nested -->
</complexType>
<element name="attributeGroup" type="attributeGroup" equivClass="schemaTop"/>
<element name="include">
<complexType content="empty" base="openAttrs" derivedBy="extension">
<attribute name="schemaLocation" type="uri-reference" minOccurs="1"/>
</complexType>
</element>
<element name="import">
<complexType content="empty" base="openAttrs" derivedBy="extension">
<attribute name="namespace" type="uri-reference" minOccurs="1"/>
<attribute name="schemaLocation" type="uri-reference"/>
</complexType>
</element>
<!-- Better reference mechanisms -->
<complexType name="keybase" base="annotated" derivedBy="extension">
<element ref="selector"/>
<element ref="field" minOccurs="1" maxOccurs="*"/>
<attribute name="name" type="NCName" minOccurs="1"/>
</complexType>
<element name="selector" type="XPathExprApprox"/>
<element name="field" type="XPathExprApprox"/>
<element name="identity-constraint" type="keybase" abstract="true"/>
<element name="unique" equivClass="identity-constraint"/>
<element name="key" equivClass="identity-constraint"/>
<element name="keyref" equivClass="identity-constraint">
<complexType base="keybase" derivedBy="extension">
<attribute name="refer" type="QName" minOccurs="1"/>
</complexType>
</element>
<simpleType name="XPathExprApprox" base="string">
<annotation>
<documentation>An XPath expression</documentation>
<documentation>A utility type, not for public use</documentation>
</annotation>
<pattern value="(/|//|\.|\.\.|:|::|\||(\c-[.:/|])+)+">
<annotation>
<documentation>A VERY permissive definition,
probably not even right
</documentation>
</annotation>
</pattern>
</simpleType>
<!-- notation element type -->
<element name="notation" equivClass="schemaTop">
<complexType base="annotated" derivedBy="extension">
<attribute name="name" type="NCName" minOccurs="1"/>
<attribute name="public" type="public" minOccurs="1"/>
<attribute name="system" type="uri-reference"/>
</complexType>
</element>
<simpleType name="public" base="string">
<annotation>
<documentation>A public identifier, per ISO 8879</documentation>
<documentation>A utility type, not for public use</documentation>
</annotation>
</simpleType>
<!-- notations for use within XML Schema schemas -->
<notation name="XMLSchemaStructures" public="structures" system="&XSP1.URI;.xsd"/>
<notation name="XML" public="REC-xml-19980210" system="http://www.w3.org/TR/1998/REC-xml-19980210"/>
</schema>
NOTE:
And that is the end of the schema for XML Schema: Structures.
B (normative) DTD for Schemas
The DTD for XML Schema: Structures is given below. Note there is no
implication here the schema must be the root element of a document.
<!-- DTD for XML Schemas: Part 1: Structures -->
<!-- $Id: structures.html,v 1.2 2000/02/25 17:46:33 connolly Exp $ -->
<!-- Note this DTD is NOT the normative structures DTD - - the
prose copy in the structures REC is the normative version (which
shouldn't differ from this one except for this comment and entity
expansions, but just in case -->
<!ENTITY % versionEntities SYSTEM "../versionInfo.ent">
%versionEntities; <!-- get path and date entities -->
<!-- The the datatype element and its components
are defined in XML Schema: Part 2: Datatypes -->
<!-- Note %p is defined in datatypes.dtd -->
<!ENTITY % xs-datatypes PUBLIC 'datatypes'
'../datatypes/datatypes.dtd' >
%xs-datatypes;
<!ENTITY % s ''> <!-- if %p is defined (e.g. as foo:) then you must
also define %s as the suffix for the appropriate
namespace declaration (e.g. :foo) -->
<!ENTITY % nds 'xmlns%s;'>
<!-- Define all the element names, with optional prefix -->
<!ENTITY % schema "%p;schema">
<!ENTITY % complexType "%p;complexType">
<!ENTITY % element "%p;element">
<!ENTITY % unique "%p;unique">
<!ENTITY % key "%p;key">
<!ENTITY % keyref "%p;keyref">
<!ENTITY % selector "%p;selector">
<!ENTITY % field "%p;field">
<!ENTITY % group "%p;group">
<!ENTITY % all "%p;all">
<!ENTITY % choice "%p;choice">
<!ENTITY % sequence "%p;sequence">
<!ENTITY % any "%p;any">
<!ENTITY % anyAttribute "%p;anyAttribute">
<!ENTITY % sic "%p;sic">
<!ENTITY % attribute "%p;attribute">
<!ENTITY % attributeGroup "%p;attributeGroup">
<!ENTITY % include "%p;include">
<!ENTITY % import "%p;import">
<!ENTITY % notation "%p;notation">
<!-- Customisation entities for the ATTLIST of each element type.
Define one of these if your schema takes advantage of the
anyAttribute='##other' in the schema for schemas -->
<!ENTITY % schemaAttrs ''>
<!ENTITY % complexTypeAttrs ''>
<!ENTITY % elementAttrs ''>
<!ENTITY % groupAttrs ''>
<!ENTITY % allAttrs ''>
<!ENTITY % choiceAttrs ''>
<!ENTITY % sequenceAttrs ''>
<!ENTITY % anyAttrs ''>
<!ENTITY % anyAttributeAttrs ''>
<!ENTITY % attributeAttrs ''>
<!ENTITY % attributeGroupAttrs ''>
<!ENTITY % uniqueAttrs ''>
<!ENTITY % keyAttrs ''>
<!ENTITY % keyrefAttrs ''>
<!ENTITY % includeAttrs ''>
<!ENTITY % importAttrs ''>
<!ENTITY % notationAttrs ''>
<!ENTITY % complexDerivationChoice "(extension|restriction|reproduction)">
<!ENTITY % complexDerivationSet "CDATA">
<!-- #all or space-separated list drawn from derivationChoice -->
<!ENTITY % blockSet "CDATA">
<!-- #all or space-separated list drawn from
derivationChoice + 'equivClass' and 'list' -->
<!ENTITY % mgs '%all; | %choice; | %sequence;'>
<!ENTITY % cs '%choice; | %sequence;'>
<!-- the duplication below is to produce an unambiguous content model
which allows annotation everywhere -->
<!ELEMENT %schema; ((%include; | %import; | %annotation;)*,
(%simpleType; | %complexType;
| %element;
| %attributeGroup; | %group;
| %notation; ),
(%annotation;
| %simpleType; | %complexType;
| %element;
| %attributeGroup; | %group;
| %notation; )* )>
<!ATTLIST %schema;
targetNamespace %URIref; #IMPLIED
version CDATA #IMPLIED
%nds; %URIref; #FIXED '&XMLSchemaNS;'
%dtnds; %URIref; #FIXED '&XMLSchemaNS;/datatypes'
finalDefault %complexDerivationSet; ''
blockDefault %blockSet; ''
id ID #IMPLIED
%schemaAttrs;>
<!-- Note the xmlns declaration is NOT in the Schema for Schemas,
because at the Infoset level where schemas operate,
xmlns(:prefix) is NOT an attribute! -->
<!-- The id attribute here and below is for use in external references
from non-schemas using simple fragment identifiers.
It is NOT used for schema-to-schema reference, internal or
external. -->
<!-- a type is a named content type specification which allows attribute
declarations-->
<!-- -->
<!ELEMENT %complexType; ((%annotation;)?,
((%facet;)*|
((%element;| %mgs; | %group; | %any;)*,
(%attribute;| %attributeGroup;)*,
(%anyAttribute;)?)))>
<!ATTLIST %complexType;
name %NCName; #IMPLIED
id ID #IMPLIED
content (textOnly|mixed|elementOnly|empty) #IMPLIED
abstract %boolean; 'false'
final %complexDerivationSet; ''
block %complexDerivationSet; ''
derivedBy %complexDerivationChoice; #IMPLIED
base %QName; #IMPLIED
%complexTypeAttrs;>
<!-- facets only if derivedBy='restriction' -->
<!-- (element|group|any) only if content=mixed or =elementOnly
and NO derivedBy at all, i.e. a root type -->
<!-- content defaults to base's if there is a complex base,
textonly if there's a simple base,
'mixed' if no base (because that's the urType's content)
and no content daughters,
'elementOnly' otherwise -->
<!-- should we replace content='empty' with content='elementOnly'
final='#all' plus no content? -->
<!-- If one top-level group, that IS the content model, otherwise
an implicit group obtains.
This is
<sequence minOccurs='1' maxOccurs='1'>
unless content='mixed', in which case it's
<choice minOccurs='0' maxOccurs='*'> -->
<!-- If anyAttribute appears in one or more referenced attributeGroups
and/or explicitly, the intersection of the permissions is used -->
<!-- A text-only type with no attributes differs from a datatype with
the same base qualified the same way in regard to the impact on
attributes of anyAttribute -->
<!-- an element is declared by either:
a name and a type (either nested or referenced via the type attribute)
or:
a ref to an existing element declaration -->
<!ELEMENT %element; ((%annotation;)?, (%complexType;| %simpleType;)?,
(%unique; | %key; | %keyref;)*)>
<!-- type or datatype only if no type|ref attribute -->
<!-- ref not allowed at top level -->
<!ATTLIST %element;
name %NCName; #IMPLIED
id ID #IMPLIED
ref %QName; #IMPLIED
type %QName; #IMPLIED
minOccurs %non-negative-integer; '1'
maxOccurs CDATA #IMPLIED
nullable %boolean; 'false'
equivClass %QName; #IMPLIED
abstract %boolean; 'false'
final %complexDerivationSet; ''
block %blockSet; ''
default CDATA #IMPLIED
fixed CDATA #IMPLIED
%elementAttrs;>
<!-- type and ref are mutually exclusive.
name and ref are mutually exculsive, one is required -->
<!-- In the absence of type AND ref, type defaults to type of
equivClass, if any, else the ur-type, i.e. unconstrained -->
<!-- maxOccurs defaults to 1 or minOccurs, whichever is greater -->
<!-- default and fixed are mutually exclusive -->
<!ELEMENT %group; (%mgs;)?>
<!ATTLIST %group;
name %NCName; #IMPLIED
ref %QName; #IMPLIED
minOccurs %non-negative-integer; '1'
maxOccurs CDATA #IMPLIED
id ID #IMPLIED
%groupAttrs;>
<!ELEMENT %all; ((%annotation;)?, (%element;| %group;| %cs; | %any;)*)>
<!ATTLIST %all;
minOccurs %non-negative-integer; '1'
maxOccurs CDATA #IMPLIED
id ID #IMPLIED
%allAttrs;>
<!ELEMENT %choice; ((%annotation;)?, (%element;| %group;| %cs; | %any;)*)>
<!ATTLIST %choice;
minOccurs %non-negative-integer; '1'
maxOccurs CDATA #IMPLIED
id ID #IMPLIED
%choiceAttrs;>
<!ELEMENT %sequence; ((%annotation;)?, (%element;| %group;| %cs; | %any;)*)>
<!ATTLIST %sequence;
minOccurs %non-negative-integer; '1'
maxOccurs CDATA #IMPLIED
id ID #IMPLIED
%sequenceAttrs;>
<!-- an anonymous grouping in a model, or
a top-level named group definition, or a reference to same -->
<!-- Note that if order is 'all', group is not allowed inside.
If order is 'all' THIS group must be alone (or referenced alone) at
the top level of a content model -->
<!-- If order is 'all', minOccurs==maxOccurs==1 on element/any inside -->
<!-- Should allow minOccurs=0 inside order='all' . . . -->
<!ELEMENT %any; EMPTY>
<!ATTLIST %any;
namespace CDATA '##any'
processContents (skip|lax|strict) 'strict'
minOccurs %non-negative-integer; '1'
maxOccurs CDATA #IMPLIED
%anyAttrs;>
<!-- namespace is interpreted as follows:
##any - - any non-conflicting WFXML at all
##other - - any non-conflicting WFXML from namespace other
than targetNamespace
##local - - any unqualified non-conflicting WFXML/attribute
one or - - any non-conflicting WFXML from
more URI the listed namespaces
references
##targetNamespace may appear in the above list, with the
obvious meaning -->
<!ELEMENT %anyAttribute; EMPTY>
<!ATTLIST %anyAttribute;
namespace CDATA '##any'
%anyAttributeAttrs;>
<!-- namespace is interpreted as for 'any' above -->
<!-- for use inside basetype to copy down corresponding content
model particle from the basetype's content model -->
<!ELEMENT %sic; EMPTY>
<!ELEMENT %attribute; ((%annotation;)?, (%simpleType;)?)>
<!ATTLIST %attribute;
name %NCName; #REQUIRED
type %QName; #IMPLIED
maxOccurs (0|1) '1'
minOccurs (0|1) '0'
default CDATA #IMPLIED
fixed CDATA #IMPLIED
%attributeAttrs;>
<!-- default and fixed are mutually exclusive -->
<!-- type attr and datatype content are mutually exclusive -->
<!-- an attributeGroup is a named collection of attribute decls, or a
reference thereto -->
<!ELEMENT %attributeGroup; ((%annotation;)?,
(%attribute; | %attributeGroup;)*,
(%anyAttribute;)?) >
<!ATTLIST %attributeGroup;
name %NCName; #IMPLIED
id ID #IMPLIED
ref %QName; #IMPLIED
%attributeGroupAttrs;>
<!-- ref iff no content, no name. ref iff not top level -->
<!-- better reference mechanisms -->
<!ELEMENT %unique; ((%annotation;)?, %selector;, (%field;)+)>
<!ATTLIST %unique; name %NCName; #REQUIRED
id ID #IMPLIED
%uniqueAttrs;>
<!ELEMENT %key; ((%annotation;)?, %selector;, (%field;)+)>
<!ATTLIST %key; name %NCName; #REQUIRED
id ID #IMPLIED
%keyAttrs;>
<!ELEMENT %keyref; ((%annotation;)?, %selector;, (%field;)+)>
<!ATTLIST %keyref;
name %NCName; #REQUIRED
id ID #IMPLIED
refer %QName; #REQUIRED
%keyrefAttrs;>
<!ELEMENT %selector; (#PCDATA)>
<!ELEMENT %field; (#PCDATA)>
<!-- Schema combination mechanisms -->
<!ELEMENT %include; EMPTY>
<!ATTLIST %include; schemaLocation %URIref; #REQUIRED
%includeAttrs;>
<!ELEMENT %import; EMPTY>
<!ATTLIST %import; namespace %URIref; #REQUIRED
schemaLocation %URIref; #IMPLIED
%importAttrs;>
<!ELEMENT %notation; EMPTY>
<!ATTLIST %notation;
name %NCName; #REQUIRED
id ID #IMPLIED
public CDATA #REQUIRED
system %URIref; #IMPLIED
%notationAttrs;>
<!NOTATION XMLSchemaStructures PUBLIC 'structures'
'&XSP1.URI;.xsd' >
<!NOTATION XML PUBLIC 'REC-xml-1998-0210'
'http://www.w3.org/TR/1998/REC-xml-19980210' >
D References (normative) *
-
Cambridge Communiqué
-
The
Cambridge Communiqué, Ralph Swick
and Henry S. Thompson, editors, 7 October 1999. See http://www.w3.org/TR/schema-arch
-
DCD
- Document
Content Description for XML (DCD), Tim Bray et al. W3C, 10 August 1998.
See http://www.w3.org/TR/NOTE-dcd
-
DDML
- Document
Definition Markup Language. See
http://www.w3.org/TR/NOTE-ddml
-
XML Schema: Exposition
-
XML Schema:
Exposition, David C. Fallside, ed. See http://www.w3.org/TR/2000/WD-xmlschema-0-20000225/
-
HTML-4
- HTML 4.0
Specification, Dave Raggett et al. W3C, 1998. See
http://www.w3.org/TR/REC-html40/
-
ISO-11404
- ISO
11404 -- Information Technology -- Programming Languages, their environments
and system software interfaces -- Language-independent datatypes,
ISO/IEC 11404:1996(E).
-
RFC-1808
- RFC
1808,Relative Uniform Resource Locators. Internet Engineering Task
Force. See http://www.ietf.org/rfc/rfc1808.txt
-
SOX
- Schema for
Object-oriented XML, Matt Fuchs, et al. W3C, 1998. See
http://www.w3.org/Submission/1998/15/
-
SOX-1.1
- Schema
for Object-oriented XML, Version 1.1, Matt Fuchs, et al. W3C, 1999. See
???
-
URI
- Uniform
Resource Identifiers (URI): Generic Syntax and Semantics. See
http://www.ics.uci.edu/~fielding/url/draft-fielding-uri-syntax-01.txt
-
URL
- RFC
1738,Uniform Resource Locators (URL). Internet Engineering Task
Force. See http://www.ietf.org/rfc/rfc1738.txt
-
URN
- RFC 2141,URN
Syntax. Internet Engineering Task Force. See
http://www.ietf.org/rfc/rfc2141.txt
-
WAI-PAGEAUTH
-
WAI Accessibility Guidelines: Page Authoring, Gregg Vanderheiden
et al. W3C, 14-Apr-1998. See http://www.w3.org/TR/WAI-WEBCONTENT/
-
WEBARCH-EXTLANG
- Web Architecture: Extensible Languages, Tim
Berners-Lee and Dan Connolly. W3C, 10 Feb 1998. See
http://www.w3.org/TR/NOTE-webarch-extlang
-
WEBSGML
-
Proposed TC for WebSGML Adaptations for SGML, C. F. Goldfarb, ed.,
14 June 1997. See http://www.sgmlsource.com/8879rev/n1929.htm
-
XML Schemas: Datatypes
-
XML Schema Part 2: Datatypes, Paul V. Biron and Ashok
Malhotra, eds. See http://www.w3.org/TR/2000/WD-xmlschema-2-20000225/datatypes.html
-
XML Schema Requirements
-
XML Schema Requirements , Ashok Malhotra and Murray Maloney, ed.,
W3C, 15 February 1999. See http://www.w3.org/TR/NOTE-xml-schema-req
-
XDR
- XML-Data
Reduced, Frankston, Charles, and Henry S. Thompson, ed. See
http://www.ltg.ed.ac.uk/~ht/XMLData-Reduced.htm
-
XLink
- XML Linking
Language (XLink), Eve Maler and Steve DeRose, W3C, 3 March 1998. See
http://www.w3.org/TR/WD-xlink
-
XML
- Extensible
Markup Language (XML) 1.0, Tim Bray, et al. W3C, 10 February 1998. See
http://www.w3.org/TR/REC-xml
-
XSLT
- Extensible
Stylesheet Language Transformations, James Clark, W3C, 21 April 1999.
See http://www.w3.org/TR/1999/WD-xslt-19990421
-
XML-Data
-
XML-Data, Andrew Layman, et al. W3C, 05 January 1998. See
http://www.w3.org/TR/1998/NOTE-XML-data-0105/
-
XML-Infoset
- XML Information Set (public WD),
David Megginson et al., W3C, 1999. See
http://www.w3.org/TR/xml-infoset
-
XML-Namespaces
-
Namespaces in XML, Tim Bray et al., W3C, 1998. See
http://www.w3.org/TR/WD-xml-names/
-
XPointer
- XML
Pointer Language (XPointer), Eve Maler and Steve DeRose, W3C, 3 March
1998. See http://www.w3.org/TR/xptr
-
XPath
-
XML Path Language, James Clark
and Steve DeRose, editors, 16 November 1999. See http://www.w3.org/TR/xpath
-
XSchema
- XSchema
Specification, Simon St. Laurent, Ronald Bourret, John Cowan, et al.,
Version 1.0, Draft, 18 October 1998. See
http://www.simonstl.com/xschema/spec/xscspecv4.htm
For more general information, consult
http://purl.oclc.org/NET/xschema
E Acknowledgements (non-normative)
The following have contributed material to this draft:
- David Fallside, IBM
- Scott Lawrence, Agranat Systems
- Andrew Layman, Microsoft
- Eve L. Maler, Sun Microsystems
The editors acknowledge the members of the XML Schema Working Group, the members of other W3C Working Groups, and industry experts in other
forums who have contributed directly or indirectly to the process or content of
creating this document. The Working Group is particularly grateful to Lotus
Development Corp. and IBM for providing teleconferencing facilities.
The current members of the XML Schema Working Group are:
David Beech, Oracle Corp.; Paul V. Biron, Health Level Seven; Allen Brown, Microsoft; Greg Bumgardner, Rogue Wave Software; Lee Buck, Extensibility; Dean Burson, Lotus Development Corporation; Charles E. Campbell, Informix; Peter Chen, Bootstrap Alliance and LSU; David Cleary, Progress Software; Dan Connolly, W3C (staff contact); Andrew Eisenberg, Progress Software; Rob Ellman, Calico Commerce; David Ezell, Hewlett Packard Company; David Fallside, IBM; Matthew Fuchs, Commerce One; Paul Grosso, ArborText, Inc; Dave Hollander, CommerceNet (co-chair); Mary Holstege, Calico Commerce; Jane Hunter, Distributed Systems Technology Centre (DSTC Pty Ltd); Renato Iannella, Distributed Systems Technology Centre (DSTC Pty Ltd); Rick Jelliffe, Academia Sinica; Dianne Kennedy, Graphic Communications Association; Setrag Khoshafian, Technology Deployment International (TDI); Setrag Khoshafian, Technology Deployment International (TDI); Ara Kullukian, Technology Deployment International (TDI); Andrew Layman, Microsoft; Dmitry Lenkov, Hewlett Packard Company; Eve Maler, Sun Microsystems; Ashok Malhotra, IBM; Murray Maloney, Commerce One; John McCarthy, Lawrence Berkeley National Laboratory; Noah Mendelsohn, Lotus Development Corporation; Don Mullen, Extensibility; Murata Makoto, Xerox; Frank Olken, Lawrence Berkeley National Laboratory; Dave Peterson, Graphic Communications Association; Mark Reinhold, Sun Microsystems; Shriram Revankar, Xerox; Jonathan Robie, Software AG; Lew Shannon, NCR; C. M. Sperberg-McQueen, W3C (co-chair); Henry S. Thompson, University of Edinburgh; Matt Timmermans, Microstar; Jim Trezzo, Oracle Corp.; Steph Tryphonas, Microstar; Mark Tucker, Health Level Seven; Asir S. Vedamuthu, webMethods, Inc; Priscilla Walmsley, XMLSolutions; Norm Walsh, ArborText, Inc; Aki Yoshida, SAP AG
The XML Schema Working Group has benefited in its work from the
participation and contributions of a number of people not currently
members of the Working Group, including
in particular those named below. Affiliations given are those current at
the time of their work with the WG.
Paula Angerstein, Vignette Corporation; Gabe Beged-Dov, Rogue Wave Software; Dean Burson, Lotus Development Corporation; George Feinberg, Object Design; Charles Frankston, Microsoft; Ernesto Guerrieri, Inso; Michael Hyman, Microsoft; Janet Koenig, Sun Microsystems; Chris Olds, Wall Data; William Shea, Merrill Lynch; Ralph Swick, W3C; Tony Stewart, Rivcom
F Tabulation of changes
$Log: structures.html,v $
Revision 1.2 2000/02/25 17:46:33 connolly
publication fixes by connolly
Revision 1.1 2000/02/25 16:49:14 connolly
ht Feb 24 21:35
Revision 1.46.1.48.2.3 2000/02/25 02:14:44 ht
more link fixes
Revision 1.46.1.48.2.2 2000/02/25 02:07:27 ht
link fixes
Revision 1.46.1.48.2.1 2000/02/25 01:12:09 ht
Merge in pre-publication edits
Revision 1.46.1.48 2000/02/24 23:03:55 ht
fixed examples brutally
spell check
rushed through stubs for all propmaps
Revision 1.46.1.47 2000/02/24 21:42:27 ht
exact->value, work on groups
Revision 1.46.1.46 2000/02/24 12:28:05 ht
noah's most recent additions
work on attributes, make content type a particle, not a group (oops)
Revision 1.46.1.45 2000/02/23 18:08:54 ht
ur-type consistency
more on complex type in c6
stubs for all props in c6
derivationChoice/Set/exactSet fussing
Revision 1.46.1.44 2000/02/23 10:06:31 ht
integrate work from Noah on ur-type cleanup, ed note removal
Revision 1.46.1.43 2000/02/22 23:10:27 ht
try identity-c for reference-c
Revision 1.46.1.42 2000/02/22 17:51:30 ht
Handle some ednotes, remove some stale in-doc issues
turn the rhetoric for chapter 4 around, so elements in repr are on
top, elaborate the reprdef content model accordingly
Finish off (?) <element> and associated src and cos
Revision 1.46.1.41 2000/02/21 17:45:45 ht
add latest from Noah,
more structure in <reprdef> to allow one elt->many components
Revision 1.46.1.40 2000/02/18 19:05:17 ht
minor cleanup for Plenary notice,
start on <element> element,
rename source to base
Revision 1.46.1.39 2000/02/18 12:27:22 ht
work on XML repr of attributes, QName stuff
incorporate Eve's and Noah's edits of yesterday
Revision 1.46.1.38 2000/02/17 10:10:07 ht
integrated changes from eve,
added names to annotations property (oops)
Revision 1.46.1.37 2000/02/16 22:10:45 ht
add annotations to every component,
start seriously on Chapter 4
Revision 1.46.1.36 2000/02/16 13:24:53 ht
integrate (with minor mods) updates from eve,
full (but complex) spec. for keyref validation
Revision 1.46.1.35 2000/02/15 14:12:02 ht
merged in edits to c.1 from eve
Revision 1.46.1.34 2000/02/14 17:59:37 ht
some ref-constr work, cleaned up some ednotes
Revision 1.46.1.33.2.1 2000/02/15 13:44:11 ht
noah's contributions of 14 Feb
Revision 1.46.1.33 2000/02/14 14:51:12 ht
working on particles vs. equiv classes
Revision 1.46.1.32 2000/02/14 12:07:05 bu
cvcs for model group, particle and wildcard
Revision 1.46.1.31 2000/02/14 08:46:52 ht
more from Noah
Revision 1.46.1.30 2000/02/12 18:10:47 ht
noahs next edits integrated, responded to
Revision 1.46.1.29 2000/02/12 16:53:52 ht
got defaults sorted out for element decls
Revision 1.46.1.28 2000/02/11 12:56:00 aqw
Integrate from Noah, add comments, value constraint for complex types, clarify language about LDG
Revision 1.46.1.27 2000/02/11 11:03:06 ht
Noah working on element decl
Revision 1.46.1.26 2000/02/10 15:00:50 aqw
another pass over 3.2, finished I think
Revision 1.46.1.25 2000/02/10 11:11:47 ht
appropriate noah's additions
Revision 1.46.1.23 2000/02/09 16:32:06 aqw
update terminology per some f2f votes, begin working through chapter 3, add null processing to element decl
Revision 1.46.1.22 2000/02/08 23:20:24 ht
fix bogus eg embedding
Revision 1.46.1.21 2000/01/27 19:09:32 aqw
a bit more cleanup of composition chapter, everybody has at least stub
properties, got field and selectors in barely, lots more <stale>
wrapping.
Revision 1.46.1.20 2000/01/27 16:00:13 aqw
began to mark non-restructured sections, some cleanup of composition
Revision 1.46.1.19 2000/01/27 10:57:14 aqw
Michael's and Noah's general editorial suggestions
Try reference-constraint for key, unique, keyref
Revision 1.46.1.18 2000/01/26 23:18:30 aqw
example reprdef, full set of reprdef stubs
Revision 1.46.1.17 2000/01/26 13:12:16 aqw
Another minor reordering in chapter 2
Brief expositions added to each subsection in chapter 2
QName reference validation stuff
Revision 1.46.1.16 2000/01/25 22:29:38 bu
final cross-references added to Chapter 3 stubs, some sics
Revision 1.46.1.15 2000/01/25 17:45:11 aqw
some work on references/QNames
Revision 1.46.1.14 2000/01/25 16:13:50 aqw
restructuring for parallelism, with lots of stubs, now complete?
Revision 1.46.1.13 2000/01/24 18:06:22 aqw
more re-ordering of chapter 3, preliminary cvcs for attr and elt decls
Revision 1.46.1.12 2000/01/22 11:11:06 aqw
detail work on complex type def details
Revision 1.46.1.11 2000/01/20 17:40:01 aqw
working seriously on complex type defn details
Revision 1.46.1.10 2000/01/20 11:25:29 aqw
move simple type to end of each section
start work on complex type defn for real in Chap. 3
introduce <eltref>.
Revision 1.46.1.9 2000/01/19 17:10:18 aqw
remove all remaining scraps == abstract syntax
cosmetic changes in chap.1
begin adding more details in chap.3
Revision 1.46.1.8 2000/01/19 15:52:07 aqw
restructure compdef and reprdef for better control
Revision 1.46.1.7 2000/01/18 17:59:00 aqw
moving towards auto-generated paradigms
Revision 1.46.1.6 2000/01/15 18:13:20 aqw
revised approach to reprdef
Revision 1.46.1.5 2000/01/15 12:56:03 aqw
new chaps 2 and 3 complete in outline
Starting on 4.[attr grp defn] as prototype for XML repr spec
Revision 1.46.1.4 2000/01/12 23:02:17 ht
Moved component type details from Chap 2 to Chap 3
Revision 1.46.1.3 2000/01/12 21:18:22 ht
replaced [prop] with <propdef>, <propref> and <xpropref>
Revision 1.46.1.2 2000/01/12 18:04:37 aqw
Finished drastic pruning and rewrite of Chapter 2
Now propose to move all the formal definitions to the new Chapter 3:
Schema Components, with sections called e.g. Attribute Declarations:
details or some such
Revision 1.46.1.1 2000/01/12 12:44:56 aqw
begin major reorg: component exposition started
Revision 1.46 2000/01/10 11:57:56 aqw
Fold in non-publ-related changes in 19991217 publication version (1.45.1.6)
Experiment with moving major examples out-of-line
Revision 1.45.1.6 1999/12/17 16:14:53 ht
one more link
Revision 1.45.1.5 1999/12/17 15:35:47 ht
reorder prevloc
Revision 1.45.1.4 1999/12/17 14:50:25 ht
link fixes
Revision 1.45.1.3 1999/12/17 14:46:51 ht
additional status prose
Revision 1.45.1.2 1999/12/17 13:33:11 ht
PWD status prose and link fixes
Revision 1.45.1.1 1999/12/17 12:26:37 ht
towards PWD
Revision 1.45.1.6 1999/12/17 16:14:53 ht
one more link
Revision 1.45.1.5 1999/12/17 15:35:47 ht
reorder prevloc
Revision 1.45.1.4 1999/12/17 14:50:25 ht
link fixes
Revision 1.45.1.3 1999/12/17 14:46:51 ht
additional status prose
Revision 1.45.1.2 1999/12/17 13:33:11 ht
PWD status prose and link fixes
Revision 1.45.1.1 1999/12/17 12:26:37 ht
towards PWD
Revision 1.45 1999/12/17 12:06:05 ht
eacute
Revision 1.44 1999/12/17 11:51:45 ht
make all example quotes double
some changes merged from pre-Nov-publ branch (1.15.1...)
Revision 1.43 1999/12/17 10:59:16 ht
minor fix in schema wrt keys
Revision 1.42 1999/12/16 15:48:08 ht
fix some refs, incorporate up-to-date schema and DTD
Revision 1.41 1999/12/16 15:40:05 aqw
describe exact, final and abstract on elements
Revision 1.40 1999/12/16 09:44:11 aqw
minor editorial
Revision 1.39 1999/12/14 16:22:46 aqw
various QName fixes
Revision 1.38 1999/12/10 18:01:42 ht
remove * where status has changed
Revision 1.37 1999/12/10 16:14:10 aqw
renaming attrGroup, elemOnly, integrate DTD and schema
Revision 1.36 1999/12/10 16:08:05 aqw
more on BRM, add an wildcard ambiguity issue
Revision 1.35 1999/12/10 10:07:35 ht
merge in new-design branch
Revision 1.34 1999/12/10 09:38:42 ht
minor orphan changes
Revision 1.33 1999/12/08 20:06:52 aqw
added prose for BRM
Revision 1.32 1999/12/03 15:49:25 ht
fix status text
Revision 1.31 1999/12/03 14:54:16 aqw
ht version confusion
Revision 1.30 1999/12/03 14:48:41 aqw
Outline inclusion of BRM proposal
Implemented QName aspect of composition decision
Revision 1.29.1.6 1999/12/08 20:04:26 aqw
describe impact of exact for equiv classes, remove substitutabiliity section
Revision 1.29.1.5 1999/12/06 23:15:09 ht
add stars, no standalone
Revision 1.29.1.4 1999/12/06 22:50:02 aqw
add equiv classes, up-to-date DTD and schema
Revision 1.29.1.3 1999/12/03 19:37:27 ht
Fill in 3.6.3, controlling derivation, including mod agreed with Allen
wrt type tolerance.
Revision 1.29.1.2 1999/12/03 15:55:38 aqw
cleanup new proposal stuff for preliminary release
Revision 1.29.1.1 1999/12/02 22:55:36 aqw
begin serious work on integrating new type derivation proposal
Revision 1.29 1999/12/02 19:05:00 aqw
resolve ! issue in <any namespace='...'> in favour of ##
remove private exploratory hierarchy rewrite
Revision 1.28 1999/12/02 11:36:27 aqw
merge in DTD and schema for internal point release
Revision 1.27 1999/12/02 11:09:36 aqw
composition tf integrates, validates nearly ok
Revision 1.26 1999/12/01 15:43:23 aqw
integrating composition tf . . .
Revision 1.25 1999/11/22 14:14:59 aqw
integrate tentative type construction compromise
Revision 1.24 1999/11/12 17:00:41 ht
Incorporate minimal null support
Revision 1.23 1999/11/11 11:19:11 ht
add issues per 1999-11-04 telcon vote
Revision 1.22 1999/11/11 11:11:51 ht
include dtd and schema
Revision 1.21.1.1 1999/11/22 14:03:55 aqw
try out type construction compromise
Revision 1.21 1999/11/05 00:48:14 aqw
note about status vis a vis forthcoming issues from minutes
Revision 1.20 1999/11/04 23:46:57 aqw
remove element classes per WG vote
Revision 1.19 1999/11/03 21:39:47 aqw
fix editors list and acks
typoes spotted by DBeech
Revision 1.18 1999/11/03 15:49:26 aqw
Implement chair's instructions wrt WG poll closed 1999-10-30:
* re-integrate named model groups
* change details of implicit openness
* remove entities, not notations
Revision 1.17 1999/11/02 23:37:35 aqw
merge refinement proposal into mainline preparatory to implementing poll results
Revision 1.16 1999/11/02 21:32:25 aqw
remove entity definitions and related material (e.g. notations)
Revision 1.15 1999/10/27 13:28:58 ht
Fix some (all?) syntax paradigms, examples
Include bug-fixed .xsd and .dtd
Revision 1.14 1999/10/27 10:48:01 ht
Incorporate up-to-date schema and DTD, completing concrete syntax changes
Parameterise paths/dates to facilitate release process
Revision 1.13.1.15 1999/10/26 16:23:30 ht
a bit more on validity
Revision 1.13.1.14 1999/10/25 14:37:31 ht
Begin to try to fill in validity section on basis of
schema-valid(EII,type,schemaSet) minimalist approach
Revision 1.13.1.13 1999/10/19 18:42:13 ht
added xsd:type to text, changed status
Revision 1.13.1.12 1999/10/18 19:46:12 aqw
Added concrete syntax, prose and examples to 3.6, new section on the
hierarchy and restrictions
Revision 1.13.1.11 1999/10/18 15:28:16 aqw
Included lots in 3.5 and 3.6, editting it in to shape
Revision 1.13.1.10 1999/10/18 13:55:23 aqw
correct and corresponding DTD and Schema included
text from new design included in 3.5 and 3.6 for editting
Revision 1.13.1.9 1999/10/18 11:39:01 aqw
light pass over section 2, cleaning up 'type' terminology
minor fixups in 3.4
Revision 1.13.1.8 1999/10/17 22:05:19 aqw
first pass through 3.4 complete
Revision 1.13.1.7 1999/10/16 22:12:03 aqw
element classes
Revision 1.13.1.6 1999/10/16 19:02:51 aqw
attribute finished, also attrGroup
Revision 1.13.1.5 1999/10/16 17:53:28 aqw
finished (?) with complex types, on to attributes
Revision 1.13.1.4 1999/10/16 11:52:07 aqw
still working on complex type
Revision 1.13.1.3 1999/10/15 16:38:31 aqw
more work on 'type'
Revision 1.13.1.1 1999/10/15 11:46:18 ht
on the way to matching new refinement proposal
Revision 1.13 1999/10/09 10:49:40 ht
correct headline date
Revision 1.12 1999/10/05 09:56:19 ht
Preliminary implementation of A3 and A7 (ampConnector and richerMixed)
votes. Moving towards a parallel syntax for elementDecl/Ref and
groupDefn/Ref.
Concrete syntax paradigms, examples, DTD and Schema NOT up-to-date
Revision 1.11 1999/09/27 16:31:07 ht
merge simple back to main branch
Revision 1.10.2.38 1999/09/27 16:29:02 ht
return to xmlschema-current as base
Revision 1.10.2.37 1999/09/24 16:40:22 ht
add comments archive pointer
Revision 1.10.2.36 1999/09/24 16:38:23 ht
link housekeeping, move TF reports bibliography to separate appendix
Revision 1.10.2.35 1999/09/24 13:44:27 ht
final (?) housekeeping before publication
Revision 1.10.2.34 1999/09/23 18:48:51 ht
changes to front matter in preparation for public WD
ponter to Simple TF included
Revision 1.10.2.33 1999/09/23 13:32:15 ht
up-to-date pointer to refinement TF report
Revision 1.10.2.32 1999/09/23 13:00:22 ht
typo in db entity
Revision 1.10.2.31 1999/09/23 12:59:04 ht
per suggestions from Ashok, some rewording of summary of Composition
TF, added issue regarding priority of instance->schema alternatives
Revision 1.10.2.30 1999/09/22 14:02:35 ht
typo in correction to 4.1
Revision 1.10.2.29 1999/09/22 13:58:39 ht
edits implementing Noah's comments
Revision 1.10.2.28 1999/09/22 08:07:07 ht
add verbatim change log at end
----------------------------
revision 1.10.2.27
date: 1999/09/21 16:26:11; author: ht; state: Exp; lines: +4 -4
added Id: to title for now
----------------------------
revision 1.10.2.26
date: 1999/09/21 16:06:08; author: ht; state: Exp; lines: +42 -244
replaced composition tf report with a summary and a pointer
----------------------------
revision 1.10.2.25
date: 1999/09/21 14:11:50; author: aqw; state: Exp; lines: +495 -111
some dates, up-to-date DTD and Schema for schemas
----------------------------
revision 1.10.2.24
date: 1999/09/21 10:50:37; author: ht; state: Exp; lines: +18 -3
supply missing content model for 'attribute' in concrete syntax
paradigm
----------------------------
revision 1.10.2.23
date: 1999/09/21 10:37:51; author: aqw; state: Exp; lines: +21 -20
define/declare consistency pass
----------------------------
revision 1.10.2.22
date: 1999/09/20 13:08:36; author: aqw; state: Exp; lines: +47 -49
track datatype content model changes,
minor wording
----------------------------
revision 1.10.2.21
date: 1999/09/16 14:55:17; author: ht; state: Exp; lines: +136 -14
header disclaimer, graveyards rescued to discharge references
----------------------------
revision 1.10.2.20
date: 1999/09/16 14:25:01; author: aqw; state: Exp; lines: +274 -1541
rip out all of 3.5, all of 4, install 'Draft Proposal' in 4
----------------------------
revision 1.10.2.19
date: 1999/09/16 12:08:59; author: aqw; state: Exp; lines: +107 -143
Clean up import/include/export, references in particular
Add archetypeRef to content models, minimally
New example of datatype+attr
----------------------------
revision 1.10.2.18
date: 1999/09/15 22:06:29; author: aqw; state: Exp; lines: +26 -3
Two clarifications following discussion with Andrew
1) what it would take to remove the two symbol spaces problem
2) How <archetype> allows either datatypeRef or contentType
----------------------------
revision 1.10.2.17
date: 1999/09/15 20:30:49; author: aqw; state: Exp; lines: +114 -105
change date, incorporate edited dtd
----------------------------
revision 1.10.2.16
date: 1999/09/15 19:52:39; author: aqw; state: Exp; lines: +90 -76
Encorporate/respond to Eve Maler's suggested edits
----------------------------
revision 1.10.2.15
date: 1999/09/13 16:14:12; author: aqw; state: Exp; lines: +306 -335
Finish consistency pass through 3.4
Brutal 'element type' -> element
----------------------------
revision 1.10.2.14
date: 1999/09/09 14:22:29; author: aqw; state: Exp; lines: +53 -56
cleanup pass, down to 3.3
----------------------------
revision 1.10.2.13
date: 1999/09/08 18:23:47; author: ht; state: Exp; lines: +41 -41
more type back to archetype
----------------------------
revision 1.10.2.12
date: 1999/09/08 18:03:06; author: aqw; state: Exp; lines: +214 -216
put archetype back in, imperfectly, I expect
----------------------------
revision 1.10.2.11
date: 1999/09/07 21:50:36; author: bu; state: Exp; lines: +124 -63
fix paradigm contexts, extend example, consolidate example in appendix
----------------------------
revision 1.10.2.10
date: 1999/09/07 16:54:39; author: aqw; state: Exp; lines: +514 -521
syntax paradigms now properly distributed, I think
----------------------------
revision 1.10.2.9
date: 1999/09/07 15:53:06; author: ht; state: Exp; lines: +5 -8
fixed minor validity errors
----------------------------
revision 1.10.2.8
date: 1999/09/07 15:31:58; author: aqw; state: Exp; lines: +288 -285
working on integrating syntax paradigms
----------------------------
revision 1.10.2.7
date: 1999/09/07 09:44:57; author: aqw; state: Exp; lines: +630 -33
added ALL concrete syntax boxes at once
----------------------------
revision 1.10.2.6
date: 1999/09/06 14:55:04; author: ht; state: Exp; lines: +35 -2
added one e: syntax exposition
----------------------------
revision 1.10.2.5
date: 1999/09/02 15:28:27; author: ht; state: Exp; lines: +6 -6
fix URLs for self, a bit
----------------------------
revision 1.10.2.4
date: 1999/09/02 12:53:34; author: aqw; state: Exp; lines: +108 -95
Added not-status-quo marks, changed e.g. String to string
----------------------------
revision 1.10.2.3
date: 1999/09/01 17:02:14; author: aqw; state: Exp; lines: +587 -977
integration of 2.3 from simple
more renaming
----------------------------
revision 1.10.2.2
date: 1999/08/23 15:32:16; author: aqw; state: Exp; lines: +730 -248
Modified simple integration to give preliminary consistency
----------------------------
revision 1.10.2.1
date: 1999/08/22 17:44:40; author: aqw; state: Exp; lines: +317 -260
Textual integration of Simple update of 1999-08-13
----------------------------
revision 1.10
date: 1999/07/20 19:47:27; author: ht; state: Exp; lines: +5 -5
branches: 1.10.2;
fixed dates, dangling reference
----------------------------
revision 1.9
date: 1999/07/19 09:31:26; author: ht; state: Exp; lines: +34 -38
David Beech: updated definition of "Schema" following WG and IG email
discussion. Changed "Schemata" to "Schemas" except where directly
quoted from Requirements doc. Clarified in 2.5 that elements and
attributes have separate symbol spaces (public comment). Fixed
assorted typos.
----------------------------
revision 1.8
date: 1999/06/23 10:00:31; author: aqw; state: Exp; lines: +1 -1
fix Id:
----------------------------
revision 1.7
date: 1999/06/23 09:51:15; author: aqw; state: Exp; lines: +28 -28
Restrict content model of 'all' in schema and dtd, change entities for
point releases
----------------------------
revision 1.6
date: 1999/06/23 09:10:01; author: aqw; state: Exp; lines: +147 -187
pushed & down to lowest level, fixed incoherent validity
definition in 6.2.3.7 to agree with the note which follows. Wrapped
validation text from 3.4 in appropriately named div4's
----------------------------
revision 1.5
date: 1999/06/21 16:31:59; author: aqw; state: Exp; lines: +569 -551
Really moved validity-oriented definitions to 6.3 (previous revision
was just housekeeping)
----------------------------
revision 1.4
date: 1999/06/21 16:25:21; author: aqw; state: Exp; lines: +45 -36
moved validity-oriented definitions to 6.3
----------------------------
revision 1.3
date: 1999/06/21 12:25:21; author: aqw; state: Exp; lines: +3540 -3650
Low-level: Normalise line ends, quotes
Editorial: Move all constraintnotes to new separate section
----------------------------
revision 1.2
date: 1999/05/27 14:13:54; author: aqw; state: Exp; lines: +2 -2
fix stylesheet and dtd urls to local versions
----------------------------
revision 1.1
date: 1999/05/23 16:51:11; author: ht; state: Exp;
branches: 1.1.1;
Initial revision
G Open Issues
A tabulation of open issues flagged above follows: