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Thursday, November 1, 2007

Converting XML Schemas to Schematron, Part 5: Validating Your Own

This Part 5 article installment continues a serialized article on
"Converting XML Schemas to Schematron." The author explained some
reasons for wanting to convert XSD to Schematron in Part 1: (1) better
diagnostics -- grammar-based diagnostics basically don't work; (2)
Schematron only needs an XSLT implementation. From Part 5: "XSD
allows you to derive your own simple datatypes by restricting the
lexical space or the value space of the type. The rule about derivation
by restriction is that everything that is valid against the derived
type is also valid against the base type. Type derivation by restriction
can be directly implemented by Schematron abstract rules. There is a
mismatch in terminology: we restrict the type (in the XSD) by extending
the constraints (in Schematron). We are not implementing simple type
derivation by union or list at the moment, because it is outside our
primary requirements. I expect derivation by list would benefit from
XPath2's extra power. Derivation by union needs more thought. But at
least this puts us in the position where I think... we can say that
Schematron's power to validate datatypes is strictly more power than
XSDs power for datatypes derived by restriction; Schematron (i.e.
using Xpath2) can express all the XSD constraints and more. But is
Schematron more powerful to model type derivation? We want to be able
to draw pretty diagrams of type derivation. Well, actually because
derivation by restriction is simply implemented by abstract rules, in
fact Schematron is equally capable of modeling the derivation structure. More Information See also XML Schema Languages: Click Here

1 comment:

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