XML Schema goes to Candidate Recommendation status

Date:       Tue, 24 Oct 2000 15:17:03 +0100
From:       "Henry S. Thompson" <ht@cogsci.ed.ac.uk>
To:         XML Developers List <xml-dev@xml.org>
Subject:    XML Schema goes to Candidate Recommendation status

The following is copied with permission of the author:

W3C is pleased to announce the advancement of the XML Schema Language
to Candidate Recommendation status.

   XML Schema Part 0: Primer, ed. David C. Fallside
   <fallside@us.ibm.com>, 24 October 2000

   XML Schema Part 1: Structures, 
   ed. Henry S. Thompson <ht@cogsci.ed.ac.uk>
   David Beech <dbeech@us.oracle.com>
   Murray Maloney <murray@muzmo.com> 
   Noah Mendelsohn <Noah_Mendelsohn@lotus.com> 
   24 October 2000

   XML Schema Part 2: Datatypes, ed.  
   Paul V. Biron <Paul.V.Biron@kp.org> and 
   Ashok Malhotra <petsa@us.ibm.com>
   24 October 2000

1 Abstracts

Part 0:

   XML Schema Part 0: Primer is a non-normative document intended to
   provide an easily readable description of the XML Schema facilities
   and is oriented towards quickly understanding how to create schemas
   using the XML Schema language. XML Schema Part 1: Structures and XML
   Schema Part 2: Datatypes provide the complete normative description
   of the XML Schema language -- this primer describes the language
   features through numerous examples which are complemented by
   extensive references to the normative texts.

Part 1:

   XML Schema: Structures specifies the XML Schema definition language,
   which offers facilities for describing the structure and
   constraining the contents of XML 1.0 documents, including those
   which exploit the XML Namespace facility. The schema language, which
   is itself represented in XML 1.0 and uses namespaces, substantially
   reconstructs and considerably extends the capabilities found in XML
   1.0 document type definitions (DTDs). This specification depends on
   XML Schema Part 2: Datatypes.

Part 2:

   XML Schema: Datatypes is part 2 of the specification of the XML
   Schema language. It defines facilities for defining datatypes to be
   used in XML Schemas and other XML specifications. The datatype
   language, which is itself represented in XML 1.0, provides a
   superset of the capabilities found in XML 1.0 document type
   definitions (DTDs) for specifying datatypes on elements and

2 Request for publication and outstanding issues

The publication is in response to the Working Group Co-Chair's request.

The last-call issues on which there was outstanding dissent are
listed (along with the other issues raised during last call)
in the Working Group chairs' summary of last-call issues.

In particular, the W3C Internationalization (I18N) WG dissented from the
specification's treatment of dates and times on several grounds:

   - The type for time durations uses years and months
     from the Gregorian calendar, and does not allow for 
        other calendar systems, such as the Hebrew calendar 
     and the Islamic calendar.
   - To avoid comparison problems (one month vs. 30 days),
        comparison between different time units has been 
        made completely indeterminate. This is unfortunate,
        as most duration comparisons (such as 1 hour to 30 
        minutes) are in fact well-defined.
  - The recurring Duration type, as well as month, year, century,
        recurringDate, and recurringDay are of limited use.

On the first objection, the director judged that for better or worse
the international community makes extensive use of the Gregorian
calendar, and there are no obvious alternatives to its use.

On the other two objections, the director judged that the concerns
raised by the I18N WG are indeed valid, but observed that a complete
reformulation of the date and time types would be a major undertaking
outside the scope of XML Schema itself at this stage.

It was decided that the best way to address these questions was through
further and wider review and testing through implementation experience,
which is what the Candidate Recommendation review is designed to
provide. Notes have been included in the specification asking for
feedback from software developers and schema authors on various aspects
of the design.

3 Exit criteria

The Candidate Recommendation period ends when the milestones below are
achieved. Currently, input from implementors is accepted at least
through 15 December 2000.

   * Sufficient reports of implementation experience will have been
     gathered to demonstrate that schema processors as described by the
     specification are implementable and have compatible behavior.
     Several partial implementations and ongoing implementation efforts
     are underway; implementors include the University of Edinburgh and
     W3C (XSV), IBM and the Apache project (Xerces), TIBCO
     Extensibility (XML Authority), XML Spy (XML Schema editor),
     and Oracle (XML Schema Processor).

   * Sufficient reports of implementation experience will have been
     gathered to reasonably address concerns that the datetime types
     interwork with other existing date time systems such as database

   * Sufficient reports of use will have been gathered to demonstrate
     that the schema language defined by the spec can usefully be
     applied in the definition of markup vocabularies and their
     applications.  In particular, it is our goal to have XML Schema
     documents defining the markup language or markup vocabulary of any
     W3C specification which currently has a DTD and which is currently
     a Candidate Recommendation, a Proposed Recommendation, or a
     Recommendation.  (N.B. it is not anticipated that these schema
     documents will in all cases mimic every feature of the
     corresponding DTDs -- in particular, the ability of a hostile user
     to modify or subvert the DTD by suitable redefinition of parameter
     entities will not necessarily be preserved.)  Some W3C specs
     already have schemas (mostly non-normative at this point), among
     them XML 1.0, XLink, SMIL, P3P, and XML Digital Signatures.

   * A formalization of XML Schema will be complete and ready for
     publication as a normative or non-normative part of the

Implementors are invited to contact the Working Group chairs to
participate in the final report.

4 Description of what Candidate Recommendation status means

The W3C Process Document describes the Candidate Recommendation status
of a specification in Section 6.2.3:

   Requirements for Entrance

     The Director must be satisfied that the Working Draft has
     successfully completed the Last Call with all comments resolved and
     that the Working Group has prepared an adequate implementation

   Associated activities

     The Working Group requests implementation experience and uses this
     to refine the specification as necessary.


     The duration is specified as part of the request for
     advancement. The duration may range from zero delay (skipped) to one

   Next State

     A Candidate Recommendation can be updated, or upon Director
     approval, advanced to Proposed Recommendation.  Otherwise it returns
     to Working Draft for further work.

   A Candidate Recommendation has received significant review from its
   immediate technical community (resulting from the Last Call).
   Advancement of a document to Candidate Recommendation is an explicit
   call to those outside of the related Working Groups or the W3C itself
   for implementation and technical feedback. There is no requirement
   that a Working Draft have two independent and interoperable
   implementations to become a Candidate Recommendation. Instead, this is
   the phase at which the Working Group is responsible for formally
   acquiring that experience or at least defining the expectations of

5 Status of This Document

The "status of this document" section for the Candidate Recommendation

   This specification of the XML Schema language is a Candidate
   Recommendation of the World Wide Web Consortium. This means that the
   XML Schema Working Groupconsiders the specification to be stable and
   encourages implementation and comment on the specification during
   this period. The Candidate Recommendation review period ends on 15
   December 2000. Please send review comments before the review period
   ends to www-xml-schema-comments@w3.org (public mailing list
   archive). Readers may find Description of changes (non-normative)
   ('J) helpful in identifying the major changes since the Last Call
   Public Working Draft.

   During the Candidate Recommendation phase, although feedback based
   on any aspect of implementation experience is welcome, there are
   certain aspects of the design presented herein for which the Working
   Group is particularly interested in feedback. These are designated
   priority feedback aspects of the design, and identified as such in
   editorial notes throughout this draft.

   Should this specification prove very difficult or impossible to
   implement, the Working Group will return the document to Working
   Draft status and make necessary changes. Otherwise, the Working
   Group anticipates asking the W3C Director to advance this document
   to Proposed Recommendation.

   This document has been produced as part of the W3C XML Activity. The
   authors of this document are the XML Schema WG members. Different
   parts of this specification have different editors.

   A list of current W3C working drafts can be found at
   http://www.w3.org/TR/. They may be updated, replaced, or obsoleted
   by other documents at any time. It is inappropriate to use W3C
   Working Drafts as reference material or to cite them as other than
   "work in progress".

World Wide Web Consortium (W3C)

Janet Daly, Head of Communications
MIT/LCS NE43-363
200 Technology Square
Cambridge, MA USA 02139

voice: +1.617.253.5884
fax:    +1.617.258.5999 

  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
            Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
                     URL: http://www.ltg.ed.ac.uk/~ht/