XML Schema goes to Candidate Recommendation status
Date: Tue, 24 Oct 2000 15:17:03 +0100
From: "Henry S. Thompson" <email@example.com>
To: XML Developers List <firstname.lastname@example.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
<email@example.com>, 24 October 2000
XML Schema Part 1: Structures,
ed. Henry S. Thompson <firstname.lastname@example.org>
David Beech <email@example.com>
Murray Maloney <firstname.lastname@example.org>
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 <email@example.com>
24 October 2000
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.
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.
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
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
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 firstname.lastname@example.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
200 Technology Square
Cambridge, MA USA 02139
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: email@example.com