A burst of schemas
09:14, 18 Dec 2002 UTC | Eric van der Vlist

For different reasons many XML 2002 presentations proposed the use of multiple validations and transformations for advanced needs, rather than using a single schema: considered too complex or even impossible to write and maintain.

Maybe influenced by my editorship of "DSDL part 1 - Interoperability Framework", I have seen the justification of such a framework coming back as a leitmotif in many presentations:

  • Liora Alschuler, in her presentation " Layered Constraints: The Proposal for HL7 Healthcare Templates," explained why, in face of the huge diversity of the practices for health reports, HL7 has chosen to associate a very lax generic schema together with templates, i.e. specific constraints which formalize the different local usages of the common schema.
  • Walter Hamscher in " XBRL: XML, XLink, and the Revolution in Corporate Reporting" explained why, for similar reasons, XBRL has chosen to express most of the structure of its reports as extended XLink link bases. Since these links cannot be validated using W3C XML Schema, to be complete the validation of XBRL documents requires a validation by the application layer that could also be performed using a language such as Schematron.
  • Gabe Beged-Dov in " Normalized Metadata Format: RDF Meets XML Schema" showed how RDF documents may be "normalized" to facilitate their validation through W3C XML Schema.
  • Eric Freese in " Using DAML+OIL as a Constraint Language for Topic Maps" proposed a modification of the syntax of XTM Topic Maps documents (which could be done by a XSLT transformation) that enables their validation using RDF applications such as OWL or DAML+OIL.
  • Bob DuCharme in " Maintaining Schemas for Pipelined Stages" has shown that the customization of generic W3C XML Schema or Relax NG schemas with added metadata could be performed through XSLT transformations more easily than using the derivation techniques of these languages.

There are few commonalities between these presentations, but all of them show how, confronted with the issue of a complex validation in very different domains, projects have chosen to split the validation of their documents into different, easier to write, elementary steps.

That's also the approach taken by DSDL, the reason why this will be a multi-part standard and the justification of its part 1, Interoperability Framework, which will define a language to describe the choreography of the elementary steps needed to perform a complex validation.

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