I'm trying to declare an element which is one of 2 complex types.

I have 2 complex types, say
However, I can't quite get the syntax down for the element declaration.
This will not validate obviously. How is it possible to achieve this?

Note: the actual types are imported from other files, I don't have control over them; otherwise I would simply rewrite the type.

Thanks.

You can copy the content models of the two types:

<xs:choice>
    <xs:sequence>
        <xs:element name="child1"/>
    </xs:sequence>
    <xs:sequence>
        <xs:element name="child2"/>
    </xs:sequence>
</xs:choice>

(actually you can omit the xs:sequence if the content models are as simple as that).

If you don't want to replicate the code, use named model groups

<xs:choice>
  <xs:group ref="g1"/>
  <xs:group ref="g2"/>
</xs:choice>

<xs:complexType name="ElemType1">
   <xs:group ref="g1"/>
</xs:complexType>

<xs:group name="g1">
   <xs:sequence>
        <xs:element name="child1"/>
    </xs:sequence>
</xs:group>



Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference

I may have mislead you about my access to the other types. These types are created by a 3rd party, and as such can change based on their needs.

So, I can't replicate the content models. Moreover, they are not declared as group s. Is there still a solution?

No, you can derive a complex type by extension from an existing type but you can't combine two types into one.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference