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Erratum

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 07 Sep 2001 13:09:42 +0100
To: www-xml-schema-comments@w3.org
Message-ID: <f5b3d5zdwxl.fsf@cogsci.ed.ac.uk>
Short summary: The elt derived from choice case of particle
restriction checking rules out the derivation of the type of <xs:all>
from xs:explicitGroup in the sForS.

Long statement:

In essence the question is, is

  <xs:sequence>
      <xs:element ref="xs:annotation" minOccurs="0"/>
      <xs:element name="element" minOccurs="0" maxOccurs="unbounded">
       . . .
      </xs:element>
  </xs:sequence>

a valid restriction of

    <xs:sequence>
     <xs:element ref="xs:annotation" minOccurs="0"/>
     <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element name="element" type="xs:localElement"/>
      <xs:element name="group" type="xs:groupRef"/>
      <xs:element ref="xs:choice"/>
      <xs:element ref="xs:sequence"/>
      <xs:element ref="xs:any"/>
     </xs:choice>
    </xs:sequence>

The recursion through sequence takes us to

      <xs:element name="element" minOccurs="0" maxOccurs="unbounded">
       . . .
      </xs:element>

vs.

     <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element name="element" type="xs:localElement"/>
      <xs:element name="group" type="xs:groupRef"/>
      <xs:element ref="xs:choice"/>
      <xs:element ref="xs:sequence"/>
      <xs:element ref="xs:any"/>
     </xs:choice>

which is covered by Elt:All/Choice/Sequence, and recurses
with

      <xs:choice>
       <xs:element name="element" minOccurs="0" maxOccurs="unbounded">
        . . .
       </xs:element>
      </xs:choice>

vs.

     <xs:choice minOccurs="0" maxOccurs="unbounded">
      <xs:element name="element" type="xs:localElement"/>
      <xs:element name="group" type="xs:groupRef"/>
      <xs:element ref="xs:choice"/>
      <xs:element ref="xs:sequence"/>
      <xs:element ref="xs:any"/>
     </xs:choice>

which fails because the max/min is in the wrong place.

I think the right solution would be to handle elt vs. choice
differently, and promote the min/max, but I'll have to think about it.

ht
-- 
  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, 7 September 2001 08:09:13 GMT

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