Question

I have an XML file and a corresponding XSD file.
In the XSD file I define a list attribute where the items in the list are part of an enumeration.

Here is an example of what I’m doing.

<xs:simpleType name="Colors">
    <xs:list itemType="ColorEnum"/>
</xs:simpleType>

<xs:simpleType name="ColorEnum">
    <xs:restriction base="xs:token">
        <xs:enumeration value="Red"/>
        <xs:enumeration value="Blue"/>
        <xs:enumeration value="Green"/>
    </xs:restriction>
</xs:simpleType>

<xs:element name="Color">
    <xs:complexType>
        <xs:attribute name="ColorList" type="Colors" />
    </xs:complexType>
</xs:element>

The XML would look something like this:

<Color ColorList="Red Blue Green"></Color>

Is there any way to make sure that the elements in the list are unique? For instance, is there any way to prevent Red from being in this list twice?

Answer 1

I think the only way is using xsd:pattern. You want:

<xs:simpleType name="ColorEnum">
 <xs:restriction base="xs:string">
   <xs:pattern value="(Red){0,1}\s(Blue){0,1}\s(Green){0,1}"/>
 </xs:restriction>
</xs:simpleType>

This should enforce also the order. I mean you can’t provide the sequence “Blue Green Red”. Anyway it should be a starting point.

---

EDIT Very nasty:

<xs:simpleType name="ColorEnum">
 <xs:restriction base="xs:string">
   <xs:pattern value="((Red)?\s(Blue)?\s(Green)?)|((Red)?\s(Green)?\s(Blue)?)|((Green)?\s(Blue)?\s(Red)?)|((Green)?\s(Red)?\s(Blue)?)|((Blue)?\s(Green)?\s(Red)?)|((Blue)?\s(Red)?\s(Green)?)"/>
 </xs:restriction>
</xs:simpleType>

---

EDIT

The number of combinations is given by the factorial of the total number of elements you use in the sequence. I hope you won’t exceed three elements then 🙂