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W3C XML Schema WG Versioning and Extensibility of Schemas and Vocabularies Noah Mendelsohn W3C XML Schema Workgroup June 22, 2005 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 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-resources.html 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-resources.html 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-resources.html 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-resources.html Some Resources Working Group Resources David Orchard is leading an • XML Schema Versioning Use Cases , ed. Hoylen Sue,Versioning DSTC Pty Ltd. analysis of XML • Framework for discussion of versioning Sperberg-McQueen for, ed. theMichael W3C Technical • An Approach for Evolving XML Vocabularies Using Group XML Schema Architecture (TAG), 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-resources.html Some Principles I. II. III. Clean support for repeated revisions (>20) Versioning SNA tied to namespaces Don’t presume constructs in instance docs: (e.g. <extension>) IV. Forward/backward compatibility SNA required: Breaking changes happen. V. Check/enforce compatibility in tools VI. Versions may or may not form sequence or tree VII. Revisions SNA expressed as deltas (see I.) SNA = Sometimes Not Always 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 don’t 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 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 Thank you!