Implementing a kind of bag element with XML schema

[Hess Yvan <yvan.hess@imtf.ch>]

I tried to implement with XML schema a kind of bag element with the
following requirements:

1. The order of the elements is not important.
2. It can contain predefined elements that must occurs with a given
occurrences (min and max). 
3. It can also accepts any kind of others elements (from the same namespace
or others namespaces) using for example <xs:any> element. 

Here are valid XML instance examples:

<metadata>
  <dc:identifier>urn:hsc:1234</dc:identifier>
  <dc:subject>this is the subject</dc:subject>
  <name>Hess Yvan</name>
  <anyOtherElement>blabla</anyOtherElement>
  <name>Hess Yvan</name>
  <dc:otherElement>blabla</otherElement>
</metadata>

<metadata>
  <dc:subject>this is the subject</dc:subject>
  <anyOtherElement>blabla</anyOtherElement>
  <dc:identifier>urn:hsc:1234</dc:identifier>
</metadata>

I would like to force that dc:identifier is always present in the metadata
element, but where this element appears is not important! This is the
requierement I have to implement.

For example, I tried somethink like that:

   <xs:element name="metadata">
      <xs:complexType>
         <xs:choice>
            <xs:element name="identifier" type="xs:string" minOccurs="1"
maxOccurs="1" />
            <xs:any processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
         </xs:choice>
      </xs:complexType>
   </xs:element>
   
But in this case it violates the "Unique Particle Attribution". Nobody can
help me to solve this problem (mailing-lists or others). I don't know if a
reach a limitation of the W3C recommendation, but from my point of view this
use case is a real concrete use case that should be supported by W3C XML
schema recommendation.

Does it exist a possibility to implement what I want to do or do I really
reach a limitation of the XML schema W3C recommendation 1.0?

Yvan Hess
Chief Software Architect

e-mail: yvan.hess@imtf.ch
phone : +41 (0)26 460 66 66 
fax   : +41 (0)26 460 66 60 

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