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Re: attribute declration's use property and restriction

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 12 Jan 2001 12:30:20 +0000
To: "Aki Yoshida" <akitoshi.yoshida@sap.com>
Cc: <www-xml-schema-comments@w3.org>
Message-ID: <f5bhf3554wz.fsf@cogsci.ed.ac.uk>
There is a constraint that you can't get rid of a required attribute
by restriction (see clause 1.3 of [1]), but neither this nor the
mapping text makes clear that the effective type must still have the
attribute as required, and no prose anywhere says whether the XML
Representation must have 'use="required"' in the restricting
definition.

As things stand the schema for schemas has a default of "optional" for 
'use', so in fact I think strictly speaking you're right that the
definition for "numFacet" you cite, namely:

<complexType name="facet">
  <complexContent>
    <extension base="annotated">
       <attribute name="value" use="required"/>
       ...
   </extension>
 </complexContent>
</complexType>

<complexType name="numFacet">
   <complexContent>
      <restriction base="facet">
         ...
         <attribute name="value" type="nonNegativeInteger"/>
      </restriction>
  </complexContent>
</complexType>

is in fact broken.  Indeed if I look at the reflected PSVI for this I
find that the 'value' attribute of numFacet is optional, although the
'value' attribute of facet is required.  It's obvious how to fix the
schema for schemas, but we should probably make a principled decision
about the XML Representation/mapping issue.

ht

[1] http://www.w3.org/TR/xmlschema-1/#coss-ct
-- 
  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
          W3C Fellow 1999--2001, part-time member of W3C Team
     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.ltg.ed.ac.uk/~ht/
Received on Friday, 12 January 2001 07:30:23 GMT

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