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From: Keith Suderman <suderman@cs.vassar.edu>
Date: Tue, 13 Jul 2004 17:22:58 -0400
Message-Id: <5.1.1.6.0.20040712200936.03526698@pop.verizonemail.net>
To: xmlschema-dev@w3.org
Hello,

I asked a similar question earlier, but I would like clarification since I 
didn't make it clear earlier that I wanted to restrict xs:anyType.

Is the following schema valid?

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
elementFormDefault="qualified" attributeFormDefault="unqualified">
         <xs:element name="root" type="empty"/>

         <xs:complexType name="empty">
                 <xs:complexContent>
                         <xs:restriction base="xs:anyType">
                                 <xs:sequence>
                                         <xs:any minOccurs="0" 
maxOccurs="0" processContents="lax"/>
                                 </xs:sequence>
                         </xs:restriction>
                 </xs:complexContent>
         </xs:complexType>
</xs:schema>


XSV 2.5, XML Spy, and Xerces-J 2.6.2 all accept this schema as valid, but 
Xerces-C 2.5 reports an error claiming that maxOccurs=0 is illegal.  When 
this was pointed out on the xerces-c list the folks there seemed 
unconvinced and replied:

 >'the derivation by restriction has some constraints, for some reference,
 >please see the following table:
 >http://www.w3.org/TR/xmlschema-0/#restrictsTable and
 >http://www.w3.org/TR/xmlschema-1/#section-Built-in-Complex-Type-Definition
 >You'll see that anyType has { minOccurs, maxOccurs } as { 1, 1 } which
 >can't be restricted.'

As I understand it, the restrictsTable referred to above (which has been 
amended in an errata [1]) only "shows several examples" of how element 
definitions may be restricted, it's not an exhaustive list of what is 
allowed.  Also, case 5.3 of [2] says "the particle of the complex type 
definition itself must be a ·valid restriction· of the particle of the 
{content type} of the {base type definition}".  In the built in complex 
type definition [3] the {particle} of the {content type} is a sequence with 
{minOccurs, maxOccurs} = {0, unbounded}, which can be restricted to {0, 0}. 
However, I'm unlikely to convince anyone on the Xerces-C list that the 
above schema is correct (or that everyone else is wrong) without some sort 
of confirmation from this list.

Finally, is

         <xs:complexType name="empty"/>

equivalent (in the sense that <root/> is the only valid document) to the 
definition above?

Thanks in advance,
Keith

References

[1] http://www.w3.org/2001/05/xmlschema-errata.html#e0-20
[2] http://www.w3.org/TR/xmlschema-1/#derivation-ok-restriction
[3] http://www.w3.org/TR/xmlschema-1/#section-Built-in-Complex-Type-Definition


--------------------------------------------------
Keith Suderman
Technical Specialist
American National Corpus
suderman@cs.vassar.edu
http://americannationalcorpus.org
Received on Tuesday, 13 July 2004 17:26:04 UTC

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