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   Re: [xml-dev] Is this allowed according to the XML Schema spec ? Tools n

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Hi Paul,

> Almost all the tools we use allow this model, except for one. And
> reading the spec I have the impression that it is indeed not
> allowed.
> It is a union using a simpletype that refers to another union.

You don't say which tool objects to this type definition nor what it
actually complains about, but if you're asking whether it's legal for
a member type of a union type to be a union type, then the answer is
yes, it's legal. In section of the XML Schema Datatypes spec
it says:

 "A ·union· datatype can be ·derived· from one or more ·atomic·,
  ·list· or other ·union· datatypes, known as the ·memberTypes· of that
  ·union· datatype."

By the way, rather than indicating the member types of a union type
using anonymous non-restricting simpleType elements nested within the
type definition, you could use the memberTypes attribute on xs:union
(this is possible because the lexical representations of the various
member types don't overlap -- there's no chance that a
termReferenceType will be confused for one of your enumerated name
tokens). Also, there's no need to set the whiteSpace facet on
xs:NMTOKEN to 'collapse' explicitly -- it's 'collapse' by default.
Perhaps this will work for you:

<schema targetNamespace="urn:mpeg:mpeg7:schema:2001"

<simpleType name="termRelationQualifierType">
  <union memberTypes="mpeg7:termReferenceType">
      <restriction base="NMTOKEN">
        <enumeration value="NT"/>
        <enumeration value="BT"/>
        <enumeration value="RT"/>
        <enumeration value="US"/>
        <enumeration value="UF"/>

<simpleType name="termReferenceType">
  <union memberTypes="anyURI">
      <restriction base="NMTOKEN">
        <pattern value=":[^:]+:[^:]+"/>




Jeni Tennison


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