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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