W3C XML Schema WG Versioning and Extensibility of Schemas and Vocabularies

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W3C XML Schema WGVersioning and
ExtensibilityofSchemas and Vocabularies

• Noah Mendelsohn
• W3C XML Schema Workgroup
• June 22, 2005

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Overview

• XML should be the key to loose coupling
• Flexible document structure
• Reasonably self-describing
• Idioms for evolving languages, vocabularies and
  schemas not agreed
• Role of namespaces
• Extension vs. restriction
• Relationship to schema documents
• Providing better support for evolving
  vocabularies is a main goal of Schema 1.1

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Some Resources

• Working Group Resources
• XML Schema Versioning Use Cases , ed. Hoylen Sue,
  DSTC Pty Ltd.
• Framework for discussion of versioning , ed.
  Michael Sperberg-McQueen
• An Approach for Evolving XML Vocabularies Using
  XML Schema , Noah Mendelsohn
• Recent minutes of the Versioning Task force
  (Member-only link), with linked references to
  earlier minutes.
• External Resources
• Editorial Draft Versioning XML Languages
  Proposed TAG Finding, ed. David Orchard and
  Norman Walsh.
• Web services or ! distributed objects?, David
  Orchard, 12 January 2004.
• Examining wildcards for versioning, David
  Orchard, 8 January 2004.
• Providing Compatible Schema Evolution, David
  Orchard, 19 January 2004.

From http//www.w3.org/2005/05/xsd-versioning-res
ources.html
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Some Resources
Schema WG is collecting and analyzing Use Cases

• Working Group Resources
• XML Schema Versioning Use Cases , ed. Hoylen Sue,
  DSTC Pty Ltd.
• Framework for discussion of versioning , ed.
  Michael Sperberg-McQueen
• An Approach for Evolving XML Vocabularies Using
  XML Schema , Noah Mendelsohn
• Recent minutes of the Versioning Task force
  (Member-only link), with linked references to
  earlier minutes.
• External Resources
• Editorial Draft Versioning XML Languages
  Proposed TAG Finding, ed. David Orchard and
  Norman Walsh.
• Web services or ! distributed objects?, David
  Orchard, 12 January 2004.
• Examining wildcards for versioning, David
  Orchard, 8 January 2004.
• Providing Compatible Schema Evolution, David
  Orchard, 19 January 2004.

From http//www.w3.org/2005/05/xsd-versioning-res
ources.html
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Some Resources
Collection of terminology and proposed mechanisms

• Working Group Resources
• XML Schema Versioning Use Cases , ed. Hoylen Sue,
  DSTC Pty Ltd.
• Framework for discussion of versioning , ed.
  Michael Sperberg-McQueen
• An Approach for Evolving XML Vocabularies Using
  XML Schema , Noah Mendelsohn
• Recent minutes of the Versioning Task force
  (Member-only link), with linked references to
  earlier minutes.
• External Resources
• Editorial Draft Versioning XML Languages
  Proposed TAG Finding, ed. David Orchard and
  Norman Walsh.
• Web services or ! distributed objects?, David
  Orchard, 12 January 2004.
• Examining wildcards for versioning, David
  Orchard, 8 January 2004.
• Providing Compatible Schema Evolution, David
  Orchard, 19 January 2004.

From http//www.w3.org/2005/05/xsd-versioning-res
ources.html
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Some Resources
White paper by Noah includes general principles
and some mechanisms

• Working Group Resources
• XML Schema Versioning Use Cases , ed. Hoylen Sue,
  DSTC Pty Ltd.
• Framework for discussion of versioning , ed.
  Michael Sperberg-McQueen
• An Approach for Evolving XML Vocabularies Using
  XML Schema , Noah Mendelsohn
• Recent minutes of the Versioning Task force
  (Member-only link), with linked references to
  earlier minutes.
• External Resources
• Editorial Draft Versioning XML Languages
  Proposed TAG Finding, ed. David Orchard and
  Norman Walsh.
• Web services or ! distributed objects?, David
  Orchard, 12 January 2004.
• Examining wildcards for versioning, David
  Orchard, 8 January 2004.
• Providing Compatible Schema Evolution, David
  Orchard, 19 January 2004.

From http//www.w3.org/2005/05/xsd-versioning-res
ources.html
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Some Resources
David Orchard is leading an analysis of XML
Versioning for the W3C Technical Architecture
Group (TAG)

• Working Group Resources
• XML Schema Versioning Use Cases , ed. Hoylen Sue,
  DSTC Pty Ltd.
• Framework for discussion of versioning , ed.
  Michael Sperberg-McQueen
• An Approach for Evolving XML Vocabularies Using
  XML Schema , Noah Mendelsohn
• Recent minutes of the Versioning Task force
  (Member-only link), with linked references to
  earlier minutes.
• External Resources
• Editorial Draft Versioning XML Languages
  Proposed TAG Finding, ed. David Orchard and
  Norman Walsh.
• Web services or ! distributed objects?, David
  Orchard, 12 January 2004.
• Examining wildcards for versioning, David
  Orchard, 8 January 2004.
• Providing Compatible Schema Evolution, David
  Orchard, 19 January 2004.

From http//www.w3.org/2005/05/xsd-versioning-res
ources.html
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Some Principles

• Clean support for repeated revisions (gt20)
• Versioning SNA tied to namespaces
• Dont presume constructs in instance docs (e.g.
  ltextensiongt)
• Forward/backward compatibility SNA required
  Breaking changes happen.
• Check/enforce compatibility in tools
• Versions may or may not form sequence or tree
• Revisions SNA expressed as deltas (see I.)

SNA Sometimes Not Always
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Restriction vs. Extension

• Restriction base schema allows all future
  content
• Wildcards validate future content
• UPA allows apps to know which content matched WC
• Weak wildcards beat UPA problems
• New wildcard matches any elements I dont know
  about in this schema
• Extension
• Base schema validates only version 1 content
• New processing modes indicate to apps which
  subset of received content would have validated

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Checking in Tools

• Allow tooling to check what content accepted by
  S1 would be rejected by S2
• Allows tools to implement flexible policies for
  users
• Decouples schema versioning from schema document
  packaging and namespaces (unless user wants to
  couple)
• Schema WG is building necessary technology for
  simplified complex type restriction anyway.

More mechanisms in http//www.w3.org/XML/2004/02/
xsdv.html
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Thank you!