
XML Schema Working Group Charter
The mission of the XML Schema Working Group, part of the
Extensible Markup Language (XML)
Activity, is to maintain and revise the XML Schema specifications,
addressing primitive data typing, structural constraints, and conformance.
End date |
31 December 2007 |
Confidentiality |
Proceedings are Member-only |
Initial Chairs |
David Ezell |
Initial Team Contacts
(FTE %: 45) |
Michael Sperberg-McQueen |
Usual Meeting Schedule |
Telcons: Weekly
Ftf: 5-6 per year |
Scope
The XML 1.0 specification defines the concepts of well-formedness
and validity; the former characteristic is very simple to check,
while the latter requires more work to check, and allows the user to define
more powerful constraints on document structure. XML validity requires that a
document follow the constraints expressed in its document type
definition, which provides the rough equivalent of a context-free
grammar for a document type.
In some contexts, there is need for constraints tighter than, looser than,
or simply different from those which can be expressed using document type
definitions as defined in XML 1.0. There is also a widespread desire for an
XML-based syntax for expressing constraints on document types, in order to
allow tools for XML documents to be used on the constraint specifications.
Validation (and schema validation in particular) provide far more than
mere authoring convenience. Recent research has shown that XML processing
systems optimized for a specific set of validation constraints (i.e. an XML
language) can out-perform standard generic processors by a wide margin.
Using a term borrowed from database terminology, the expression of
constraints on a document type is called (in this document, at least) a
schema. (Note that the term schema has two plurals,
schemas and schemata; we use the former.)
The XML Schema working group will maintain and revise the XML Schema
specification developed beginning in 1998 and published as a W3C
Recommendation on 2 May 2001. The XML Schema specification addresses several
topics relevant to users of XML:
- primitive data typing: XML Schema defines
a type system for integers, dates, and the like, based on experience with
SQL, Java primitives, etc.
- structural constraints: XML Schema
provides a mechanism roughly analogous to DTDs for constraining document
structure (order, occurrence of elements, attributes). XML Schema differs
from DTDs in expressing these constraints in the form of an XML document,
rather than in a special-purpose ad hoc notation. Unlike DTDs, which
contain declarations both for the logical structure of elements and
attributes, and for the physical structure of entities, XML Schema
provides declarations only for constraining elements and attributes;
entity declarations continue to use DTD syntax. In addition to
DTD-like functionality, XML Schema:
- is integrated with namespaces;
- allows incomplete constraints on the content of an element type in
the form of wildcards, so-called ‘black box’ validation, and
so-called ‘white box’ validation;
- is integrated with primitive data types;
- defines inheritance for datatypes;
- provides various hooks for safe adaptation and reuse of
schemas.
- conformance: XML Schema defines the relation of schemas to XML
document instances and specifies the obligations of schema-aware
processors.
Technical areas relevant to the work under this charter include:
- the systematic development, documentation, and publication of test
cases for XML Schema
- a co-constraint language for XML Schema.
- mechanisms and guidelines for facilitiating XML Schema versioning.
- use cases and requirements for a possible XML Schema 1.2
- schema annotation and the specification of mappings which allow
software to translate data from XML document instances which conform to a
given schema into other formalisms or data models, such as
application-specific data structures, generic data structures (e.g.
relational tables), the entity-relationship model, and RDF. This work
follows on from the discussions reported in the Cambridge Communiqué of
1999, with the aim of showing how the goals described there can be
achieved.
- interoperability of schemas, data governed by them, and software, as
user vocabularies evolve (in cooperation with the XML Schema Patterns for
Databinding WG).
- the framework and interoperability rules which should govern evolution
of the XML Schema language
- interoperability with other schema languages such as RELAX-NG and
Schematron
- examination of specific use cases for XML Schema (such as composing RDF
identifiers) and technical discussion of possible solutions.
Goals
The goals of the work group in the period described by this charter are as
follows:
- to finish publication of version 1.1 of the XML Schema Recommendation,
which corrects known errors and makes modest improvements to the
language, and do preparatory work for a possible version 1.2. Changes in
function or syntax incompatible with XML Schema 1.0 have been / will be
made only if the resulting improvements compellingly justify the loss of
interoperability with existing systems and documentation. Some
substantive changes have been made in the interests of aligning version
1.1 with the needs of the XML Query 1.0, XPath 2.0, and XSLT 2.0 family
of specifications and with XML 1.1. Requests for substantive changes may
also come from other groups.
- to maintain and support XML Schema 1.0, XML Schema 1.1, and future
versions of each specification. The Working Group has published Errata in
Bugzilla containing corrections of identified errors and clarifications
of points which experience shows are obscure to careful readers.
Corrected re-editions of XML Schema 1.0, XML Schema 1.1, and future
versions are also expected.
- to finalize and publish the document XML Schema: Component
Designators
- as needed and feasible, to clarify related problem areas, and do
technical work leading possibly to Notes on technical questions connected
with the design, implementation, use, and uptake of the XML Schema
specifications; some problem areas of concern are listed below.
- to cooperate with other W3C working groups and assist them in
exploiting XML Schema for their work and adding schema-awareness to their
specifications where appropriate; this will include work on the problem
of schema-annotation and the problem of mapping from the XML vocabularies
defined by a schema into target data models
- to publish documents that provide outreach and education in support of
the XML Schema specifications, possibly including Notes on “best
practices” and “how-to” for specific problems, for instance “how
to compose RDF identifiers.”
- to work on and possibly publish a version of XML Schema 1.0 or XML
Schema 1.1 syntax that is easier to author without any special tools.
Success Criteria
The Working Group expects to demonstrate at least 2 interoperable
implementations of all required and optional features before requesting to
advance to Proposed Recommendation.
Deliverables
A set of W3C
Recommendations for:
The Working Group may decide to publish XML Schema 1.1 with only the
datatypes section, and postpone any changes to XML Schema: Structures until a
possible fuuture version 1.2.
The following document will become Working Group Notes:
Other Deliverables
- Errata list for XML Schema version 1.0 and XML Schema 1.1, with new
editions of the 1.0 and 1.1 specification as needed
- Interoperability test suite for the specifications, intended to assess
the accuracy of the Candidate Recommendations, and to promote
interoperability.
Milestones
Milestones
Note: The group will document significant
changes from this initial schedule on the group home page. |
Specification |
FPWD |
LC |
CR |
PR |
Rec |
XML Schema 1.1 Datatypes |
N/A |
N/A |
April 2007 |
August 2007 |
October 2007 |
XML Schema 1.1 Structures |
N/A |
November 2006 |
April 2007 |
August 2007 |
October 2007 |
Timeline View Summary
- August 2006: face-to-face meeting, hosted by Microsoft, WA, USA.
- November 2006: XML Schema 1.1 Structures LC
- April 2007: XML Schema 1.1 Datatypes and Structures CR
- August 2007: XML Schema 1.1 Datatypes and Structures PR
- October 2007: XML Schema 1.1 Datatypes and Structures REC
Dependencies
W3C Groups
XML has become a strategic technology in W3C and elsewhere. The
deliverables of the XML Schema Working Group must satisfy the dependencies
from other W3C Working Groups. Some dependencies to and from other W3C
Working Groups will require close cooperation during the development process;
history has shown that the requirements posed for the Schema work by these
Working Groups may change substantially during the development process, which
means the interdependency of the Schema work with these Working Groups must
be managed actively:
- XML Query Working
Group
- The XML Query Working Group expects to use schema-related information
in the processing of queries; we will discuss points of mutual interest
in an effort to ensure that XML Schema provides the information Query
needs. In particular, the XML Query Working Group has expressed
particular interest in the definition of the post-schema-validation
infoset (PSVI). The XML Schema Working Group will continue to
collaborate with XML Query and XSL in work on operators for XML Schema
datatypes and (as appropriate) on the integration of support for the
XML Schema type inventory into future versions of XPath. An important
goal of XML Schema 1.1 will be to align its type system more fully with
the needs of the XML Query language and related specifications. Work on
XQuery 1.1, updates, and full-text search may raise schema-related
problems, and the Working Groups will cooperate in resolving them.
- XSL Working Group
- In collaboration with the XML Query Working Group, the XSL Working
Group expects to make future versions of XPath and XSLT support
schema-related information, specifically type information. The XML
Schema Working Group will continue to collaborate with XML Query and
XSL in work on operators for XML Schema datatypes and (as appropriate)
on the integration of support for the XML Schema type inventory into
future versions of XPath. An important goal of XML Schema 1.1 will be
to align its type system more fully with the needs of the XSLT and
XPath 2.0 languages and related specifications.
- XML Core Working
Group
- The XML Schema work defines methods for specifying constraints on XML
documents; those constraints should apply to objects and properties
identified as significant by the XML Information Set specification.The
XML structural schema specification uses namespaces to combine
fragmentary structural specifications; it also defines
schema-validation for documents using namespaces. (In short: the XML
Schema work is namespace-aware.)
- Internationalization
Working Group
- Since XML Schema is expected to be an important tool for the
definition of markup vocabularies, it may have follow-on effects on a
larger number of people than create XML Schema documents directly. The
XML Schema Working Group and the Internationalization Working Group
will work together to clarify and resolve internationalization and
localization issues in XML Schema, and will jointly ensure that it
satisfies W3C goals for international access to the Web.
- Web Services Working
Groups
- XML Protocol and Web Services Description Language specified in the
Web Services Activity use XML Schema extensively. The newly formed "XML
Schema Patterns for Databinding Working Group" is working to produce
specifications to ease interoperability in Web Services where XML
Schema is involved. The XML Schema Working Group will ensure that the
schema language is sufficient to meet the requirements of deliverables
from these Web Services Working Groups. The XML Schema Working Group
will also discuss points of mutual interest and will review
deliverables from the Web Services Working Groups and provide them with
feedback.
Some other work groups should be mentioned here; there are no requirements
for co-development of features with these Working Groups, but there are
points of contact between their work and that of this Working Group, and thus
logical dependency between their deliverables and those of this Working
Group. Requirements from these Working Groups are expected to be well suited
for communication via documents.
- WAI Protocols & Formats
Working Group
- Reuse of common constructs greatly facilitates accessibility; the WAI
PF Working Group will review work on structural schemas to be sure
cost/benefit design decisions are informed of the benefits of
accessibility.
Formal liaison between the XML Schema Working Group and other W3C Working
Groups, including the other XML Working Groups and the WAI (Web Accessibility
Initiative) group, as well as organizations outside of the W3C, shall
normally be accomplished by the exchange of documents (requirements, reviews,
etc.) transmitted through the XML Coordination Group.
When approved by the XML Coordination Group, liaison with other W3C
Working Groups can be accomplished through direct exchange of documents or by
joint task forces. It is expected that this be required for liaison with at
least the XML Query, XSL, and Internationalization Working Groups.
External Groups
- ISO/IEC JTC1 SC34
- This group is responsible for ISO/IEC 19757 DSDL (Document Schema
Definition Languages). In particular since Schema 1.0 datatypes are
used by RelaxNG, and RelaxNG might want to use the 1.1 data types as
well.
Participation
To be successful, the XML Schema Working Group is expected to have 6 or
more active participants for its duration. Effective participation to XML
Schema Working Group is expected to consume half work day per week for each
participant; two days per week for editors. The XML Schema Working Group will
allocate also the necessary resources for building Test Suites for each
specification.
Participants are reminded of the Good
Standing requirements of the W3C Process.
Communication
This group primarily conducts its work on the Member-only mailing list
w3c-xml-schema-wg@w3.org (archive).
Information about the group (deliverables, participants, face-to-face
meetings, teleconferences, etc.) is available from the XML Schema Working Group home
page.
Patent Policy
This Working Group operates under the W3C Patent Policy
(5 February 2004 Version). To promote the widest adoption of Web standards,
W3C seeks to issue Recommendations that can be implemented, according to this
policy, on a Royalty-Free basis.
For more information about disclosure obligations for this group, please
see the W3C Patent Policy
Implementation.
About this Charter
This charter for the XML Schema Working Group has been created according
to section
6.2 of the Process
Document. Except as specified in this charter, the Working Group follows
the Common Procedures for XML Working Groups.
In the event of a conflict between this document, the common procedures, or
the provisions of any charter and the W3C Process, the W3C Process shall take
precedence.
Please also see the previous
charter for this group.
Michael Sperberg-McQueen, Team Contact
Copyright©
2006 W3C ® (MIT , ERCIM
, Keio), All Rights
Reserved.
$Date: 2007/02/12 19:16:17 $