XML schema restrictions

[botsGuy]

hi there,

I want to have an abstract type:

<xs:complexType name="itemType" abstract="true">
<xs:attribute name="key" type="xs:string"use="required">
</xs:complexType>

And then extend types with possibly more attributes and
at the same time restrict the type of data inside the element.

For example:

In the XML I would have something like:

<stringItemType key="X" otherAttr="Y"> blah </stringItemType>

The schema should restrict 'blah' to type xs:string and
extend the itemType to have an extra attribute.

I don't see how you are supposed to restrict the data
inside an element to a type in this case.

cheers,

James