Extensibility for enumerations

["Tom Doman" <TDoman@novell.com>]

We have been corresponding with an individual at Objective Systems who is working on the ASN.1 to XML Schema conversion tool we discussed in the last conference call.  I believe he may have joined the DSML group now too.  We discussed the extensibility of enumerations in XML Schema and he said that through the use of xsd:union and the memberTypes attribute this could be done.  As far as I understand it, he said that the use of the memberTypes attribute would render the xsd:restrictions listed in the xsd:enumerations as the "known" values at the time but they would not limited to those.  It sounds reasonable to us but, as I think is well documented here, we are no XML Schema experts.  Can anyone corroborate this?  Also, can anyone suggest a good free XML Schema structure checker?

If this is correct, going back to the DsmlModification from DSML v.2, a 2.1 implementation might look something like this:

 

 <xsd:complexType name="DsmlModification">
  <xsd:sequence>
   <xsd:element name="value" type="DsmlValue" minOccurs="0" maxOccurs="unbounded"/>
  </xsd:sequence>
  <xsd:attribute name="name" type="AttributeDescriptionValue" use="required"/>
  <xsd:attribute name="operation" use="required">

   <xsd:union memberTypes="xsd:string">
    <xsd:simpleType>
     <xsd:restriction base="xsd:string">
      <xsd:enumeration value="add"/>
      <xsd:enumeration value="delete"/>
      <xsd:enumeration value="replace"/>
     </xsd:restriction>
    </xsd:simpleType>

   </xsd:union>
  </xsd:attribute>
 </xsd:complexType>

This, of course, doesn't solve the association of the operation types with different "value" types as did my earlier example but it would allow additional xsd:strings to be specified as the operation.  If this construct achieves extensibility for enumerations then XML attributes aren't as restrictive as we thought and this would address some of the problems we had with the 2.0 specification.  Comment?  Questions?  Insights?

 

Thanks,

Tom Doman

tdoman@novell.com