Question

I am designing a new XSD to capture points information from a business partner. For each transaction the partner must provide a value of points for at least one points type. I have the following:

<xs:element name="Points">
   <xs:complexType>
      <xs:sequence>
         <xs:element name="SKUPointsQty" type="xs:int" minOccurs="0"/>
         <xs:element name="WelcomePointsQty" type="xs:int" minOccurs="0"/>
         <xs:element name="ManualPointsQty" type="xs:int" minOccurs="0"/>
         <xs:element name="GreenPointQty" type="xs:int" minOccurs="0"/>
      </xs:sequence>
   </xs:complexType>
</xs:element>

The business rules are:

• a transaction must provide points from one or more of the points type
• a transaction cannot provide more than one instance of the same points type

What I have so far is not ideal because it would be possible to provide an XML instance without any points. I can’t use a choice element because it must be possible to provide an XML instance with more that one points type element. The same point type must not be repeated for a single transaction.

Is it possible to enforce this rule in the design of the XSD?

I have a copy of the excellent XML Schema Companion by Neil Bradley. I can’t find the answer in there so I guess it’s not possible but thought I’d share the puzzle!

Thanks

Rob.

Answer 1

I think this kind of constraint logic is beyond XSD. Here are three techniques for checking instance documents for constraints that are not expressable by XML Schemas.