W3C home > Mailing lists > Public > public-xml-processing-model-wg@w3.org > June 2008

schema-aware XPath processing in XProc

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Thu, 26 Jun 2008 17:27:11 +0100
To: public-xml-processing-model-wg@w3.org
Message-ID: <f5bod5o17s0.fsf@hildegard.inf.ed.ac.uk>

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The good news:  The so-called 'winged horse' _does_ work for us:

 "An unknown schema type might be encountered, for example, if a
  source document has been validated using a schema that was not
  imported into the static context. In this case, an implementation is
  allowed (but is not required) to provide an _implementation-dependent
  mechanism_ for determining whether the unknown schema type is derived
  from the expected schema type. For example, an implementation might
  maintain a data dictionary containing information about type
  hierarchies." [1] [emphasis added]

So XProc implementations can, and I hope will, preserve type hierarchy
information along with the PSVI when they can.

The bad news: XPath processors don't _have_ to do this (I suppose we
could require it. . .), and in any case it doesn't cover substitution
groups :-(

My current inclination: either go ahead and support p:import-schema,
or, at the very least, make a change to the definition of the in-scope
schema definitions in the static context to be implementation-defined,
with the comment "Implementations SHOULD make information from all the
schemas used in upstream schema validation steps available via this
property".  This would essentially mandate support for the winged
horse.

ht

[1] http://www.w3.org/TR/xpath20/#id-sequencetype-matching
- -- 
       Henry S. Thompson, School of Informatics, University of Edinburgh
                         Half-time member of W3C Team
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
                       URL: http://www.ltg.ed.ac.uk/~ht/
[mail really from me _always_ has this .sig -- mail without it is forged spam]
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Received on Thursday, 26 June 2008 16:27:48 GMT

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