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   Re: XML-Data Questions

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  • From: ht@cogsci.ed.ac.uk (Henry S. Thompson)
  • To: xml-dev@ic.ac.uk
  • Date: 09 Feb 1998 12:45:01 +0000

"Don Park" <donpark@quake.net> wrote on 30 Jan (sorry for late reply):

> I have some questions about the XML-Data spec which affects implementation:
> 1. How are the schemas referenced from XML documents?

Not clear.  Given the NON-official status of XML-Data, a PI seems the
most likely route for now.

> 2. How does one validate XML documents which use XML-Data schema rather than
> DTD?

One doesn't :-)  See previous discussion on this list about validation
-- 'valid' is predicate over document instances and doctypes AS
SPECIFIED IN THE XML SPECIFICATION.  The following extract from my
SGML97 paper (cf. http://www.ltg.ed.ac.uk/~ht/B9H.html) is relevant:

"In our approach, we envisage

 a) the schema DTD, a definition of an XML representation of document
 structure, that is, an old-style DTD for schemata;

 b) a master XML application, the equivalent of the XML parser, which
 is capable of processing pairs of XML documents, where the first, a
 schema, is valid in terms of the schema DTD; the second, an instance,
 has no old-style DTD, but is both well-formed in the XML sense and
 meta-valid in terms of the schema expressed by the first.

 Meta-validity is, of course, [conformance] to the document
 structure constraints contained in the associated schema, which
 [itself is valid per] the schema DTD."

> 3. Current XML-Data does not allow or rather make it easy for enumerated
> attribute values to contain spaces becuase space is used as delimeters.
> Why not use the following structure to define enumerated attribute values?
> <elementType id="Book">
>   <attribute name="ageGrp" type="ENUMERATION">
>     <value>children</value>
>     <value>adult</value>
>     <default>adult</default>
>   </attribute>
> </elementType>

Um, the Enumeration declared value for attributes must consist of
Nmtokens (production 59 in the Proposed Recommendation) so the issue
doesn't arise.  Support for enumerated notation values isn't in
XML-Data yet (if I remember right) but the same constraint obtains there.

Hope this helps.

Henry S. Thompson, Human Communication Research Centre, University of Edinburgh
      2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
               Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk  
                      URL: http://www.cogsci.ed.ac.uk/~ht/

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