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Rick Jelliffe scripsit:
> So schema languages will
> typically have a workaround mechanism: they will have two public
> identifiers--a persistant one to let you know the genus and a specific
> one to let you know which schema to use in the particular phase
> (this is is of course the SGML Formal Publid Identifier versus
> System Identifier split, which we can see in the schemaLocation
> attribute of XML Schemas too, for all intents and purposes.)
RNG solves this problem by not having any such labels in the instance.
One validates a document when one pleases, against whatever schema
is appropriate at the time. There is no notion of *THE* schema.
AFAIK, Schematron's phases are pretty much a way of writing
multiple schemas in a single document, with inheritance from
a proto-schema (the phaseless rules). (This description is not
meant to be negative.)
Emulating this in RNG is straightforward: one writes a partial
schema containing the universally valid rules, and imports it
into the various schemas to be used at various phases.
> For publishing, where
> there is often a division of labour in the markup team, the lack of
> phases has made specialization more difficult: the table queen cannot
> say "just validate the tables, don't give me validation errors
> about the metadata--we know we have not completed that yet!"
It is straightforward, given an RNG fragment that describes the
table format, to plug it into a dummy schema that says "Anything
is allowed to hold tables, and anything is allowed in a table
cell, but tables themselves must have all the appropriate
elements, attributes, etc."
> But still it is clunky because the
> constraints are not gathered together and named by their phase.
That can be managed through the file system that contains these
different schemas.
--
John Cowan http://www.ccil.org/~cowan cowan@ccil.org
To say that Bilbo's breath was taken away is no description at all. There
are no words left to express his staggerment, since Men changed the language
that they learned of elves in the days when all the world was wonderful.
--_The Hobbit_
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