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Sorry, I meant to write
"As I understand it, NRL does not currently provide in itself any way to apply, say,
Schematron as a function on the output of a WXS transformation/validation."
By the way, James' new implementation of Schematron 1.5 looks pretty nice. I especially
like it that he seems to have implemented the assert/@subject attribute, which allows
error messages to be linked to a troublesome location with a finer grain than
the default (the rule/@context node is usually but not always the subject of the assertion.)
Schema languages are looking pretty good now. ISO DSDL is looking very healthy
and attractive, and the distant W3C XML Schemas 1.1 will undoubtedly reach giddying
I also like that James has added support for WXS to Jing. This will help people
who want to use NRL to tie together WXS and Schematron, for example, or
who have legacy WXS schemas they want to use alongside with analgesic RELAX
NG schemas. I hope W3C Schema WG might consider adopting NRL as a way
forward for future, less monolithic versions of WXS.
NRL's benefit is that allows you to use closed schemas as if they were open,
but in a controlled way. Rather than making openness or closedness a property
of the individual schema (and hence always sooner-or-later wrong), it is can be a
property of the validation-candidate selection language. So you can take a closed
XHTML schema and add in SVG elements without having to worry about adjusting the
schemas for HTML to be open or without having to re-jib the SVG schema
to allow non-SVG elements at the top-level.
I didn't get the importance of this until the last few weeks: Arjun's thread on
"what use are namespaces?" really brought it out to me. With NRL, it seems we
have a major new way to approach namespaces and schemas to get more of
XML Namspaces' advertised benefits for modularity. It is pretty exciting.