W3C Architecture DomainXML | Member-Confidential!

Charter of the XML Schema Working Group

[June 2004]

David Ezell, chair
C. M. Sperberg-McQueen and Henry Thompson, Team contacts
$Revision: 1.52 $ of $Date: 2004/06/16 18:55:46 $ by $Author: plehegar $

The XML Schema Working Group is a Working Group of the W3C and follows the working group process described in the W3C Process Document. Except as outlined elsewhere in this charter, the Working Group follows the Common Procedures for XML Working Groups.

This is the charter for this Working Group. It extends and supersedes the Working Group's previous charter.

  1. Scope
  2. Deliverables and Schedule
  3. Relationship with Other Activities
  4. Working Group participation
  5. Communication
  6. Confidentiality
  7. Face-to-Face Meetings
  8. Patent Policy

1. Scope

The XML 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. 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.

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:


The goals of the work group in the period described by this charter are five-fold:

Additional areas of work

In addition to work directly related to XML Schema 1.1, technical areas relevant to the work under this charter include:

Parallelism of work on 1.1 and preliminary discussion of 2.0

The XML Schema Working Group has repeatedly experienced tension between the desire to explore some proposal for a relatively major change in the design of the XML Schema language, and the desire to have a non-proprietary specification available for use as soon as possible. In order to allow adequate time for consideration of possible major changes in approach, the Working Group may (time permitting) do technical work on proposals intended for future versions of XML Schema (such as those listed above) in parallel with its work on XML Schema 1.1.

2. Deliverables, Milestones, and Schedule


The XML Schema Working Group has three main deliverables:

In addition, there are several other deliverables:

Milestones and schedule

Listed here are the major expected milestones for the Working Group's deliverables; for a summary of the current target dates for these milestones, see the XML Schema Working Group home page.

Milestones for XML Schema 1.1:

Milestones for XML Schema 1.0 errata:

Milestones for XML Schema: Component Designators:

Milestones for work on XML Schema 2.0:

Milestones for work on XML Schema: Formal Description:

Milestones for work on XML Schema test collections:

Note that public working drafts will be made available at least once every three months, in accordance with the W3C Process.

Expected schedule:

For details of dates and locations of face to face meetings, see the Working Group home page.

The expiration date of this charter is 30 June 2006.

3. Relationship with Other Activities

XML has become a strategic technology in W3C and elsewhere. The deliverable 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; the requirements posed for the Schema work by these Working Groups may change 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, in particular types. 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.
HTML and XForms Working Groups
It is a goal of the XML Schema work to ensure that the schema language we define will suffice for the requirements of current and future versions of the HTML specification and XForms.
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.
RDF Core Working Group
The RDF Core Working Group is preparing a new version of RDF Schema, which will use and build upon XML Schema datatypes. The RDF Core Working Group is also chartered to "provide an account of the relationship between RDF and the XML family of technologies (particularly Schemas ...)". RDF has also expressed particular interest in the problem of schema annotation and will be asked to provide feedback on the work the XML Schema Working Group does in that area.
Web Services Working Groups
The XML Protocol Working Group and the Web Services Description Working Group in the Web Services Activity use XML Schema extensively. The Web Services Choreography Working Group is working in an area which may be expected to raise complex questions for type systems and schemas. 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, and, where appropriate, direct liaison with task forces such as the Semantic Web Best Practicies Working Group XML Schema Datatypes and Semantic Web Task Force.

4. Working Group participation

To be successful, we expect the XML Schema Working Group to have 15 or more active participants for its duration. Participation is expected to consume one to two days per week of each participant's time, though the time commitment for the chair and editors may be higher. The list of members and details about joining are on the group home page.

The level of participation expected for this Working Group suggests that representatives be experts in the development or exploitation of schemas for XML-based markup languages. In addition to the time commitment noted above, each participant of the Working Group will be expected to show evidence to the Chair, each six months, of active work in the general topic area. Such active cultivation may take the form of:


The initial Chair of the XML Schema Working Group is David Ezell, National Association of Convenience Stores.

W3C Team resources

The initial W3C Team contacts for this Working Group are C. M. Sperberg-McQueen and Henry Thompson. It is expected that this Working Group would consume about 0.9 FTE, including administrative logistics.

5. Communication

The XML Schema Working Group shall communicate among its participants using the w3c-xml-schema-wg mailing list and with the other XML Working Groups through the w3c-xml-plenary@w3.org mailing list. Both lists are archived.

The XML Schema Working Group communicates with the public through the www-xml-schema-comments and xmlschema-dev mailing lists, both of which are public.

6. Confidentiality

The proceedings of this working group are Member-confidential. In support of public accountability, the Working Group will periodically make public a summary of all technical decisions made since the last public summary, and the rationales for these decisions.

7. Face-to-Face Meetings

Face-to-face meetings will be held as needed; it is expected that such meetings will be held about every two to three months.

8. 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.

Chair, W3C XML Schema Working Group: David Ezell
W3C Team contacts: C. M. Sperberg-McQueen and Henry Thompson
Last Modified: $Date: 2004/06/16 18:55:46 $