Allow bags in AttributeAssignments (multi-valued)

[cdanger]

The sections 5.39 and 5.40 of XACML 3..0 spec say:

If the <AttributeAssignmentExpression> evaluates to a bag, then there MUST be a resulting <AttributeAssignment> for each of the values in the bag.

This means that if an attribute A is assigned 10 values, you need 10 <AttributeAssignment> elements with the same AttributeId, Category and Issuer in the response. This adds to the verbosity of XACML responses and it is far from optimal from a parser's point of view.

So the proposal here is to support multiple values per AttributeAssignment, like Attributes. Also based on the discussion in issue #46, we add the DataType to AttributeAssignment (and remove from AttributeValue), and based on #18, the Category attribute is renamed CategoryId:

<xs:complexType name="AttributeAssignmentType">
	<xs:sequence>
             <xs:element ref="xacml:AttributeValue" maxOccurs="unbounded"/> 
        </xs:sequence>
	<xs:attribute name="AttributeId" type="xs:anyURI" use="required"/>
	<xs:attribute name="CategoryId" type="xs:anyURI" use="optional"/>
	<xs:attribute name="Issuer" type="xs:string" use="optional"/>
        <xs:attribute name="DataType" type="xs:anyURI" use="required"/>
        <!-- Not forgetting that we might make DataType default to string. -->
</xs:complexType>

[steven-legg]

Agreed.

AttributeAssignmentType becomes AttributeType with the addition of the CategoryId XML attribute so AttributeAssignmentType could be derived from AttributeType.

[cdanger]

Indeed, with the new AttributeType definition from #46, we can simplify 👍:

<xs:complexType name="AttributeAssignmentType">
   <xs:complexContent>
	<xs:extension base="xacml:AttributeType">
	   <xs:attribute name="CategoryId" type="xs:anyURI" use="optional"/>
       </xs:extension>
   </xs:complexContent>
</xs:complexType>

[cdanger]

Using the new Identifer type for CategoryId, the new schema:

<xs:complexType name="AttributeAssignmentType">
   <xs:complexContent>
	<xs:extension base="xacml:AttributeType">
	   <xs:attribute name="CategoryId" type="xacml:IdentifierType" use="optional"/>
       </xs:extension>
   </xs:complexContent>
</xs:complexType>

Fixed in 5bf6cc4