No, you can't put constraints on one attribute based on the value of
another attribute, not with the W3C XSD schema language.

Hi Adam,

XML Schema allows you to specify the type of an element in the instance
using the schema instance type attribute, xsi:type. Here it is a sample
schema and a valid instance that shows that.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 <xs:element name="Items">
   <xs:complexType>
     <xs:sequence maxOccurs="unbounded">
       <xs:element ref="Item"/>
     </xs:sequence>
   </xs:complexType>
 </xs:element>
 <xs:element name="Item" type="AbstractItemType"/>
 <xs:complexType name="AbstractItemType" abstract="true"/>
 <xs:complexType name="myType">
   <xs:complexContent>
     <xs:extension base="AbstractItemType">
       <xs:attribute name="len" type="xs:integer"/>
     </xs:extension>
   </xs:complexContent>
 </xs:complexType>

 <xs:complexType name="NOTmyType">
   <xs:complexContent>
     <xs:extension base="AbstractItemType">
     </xs:extension>
   </xs:complexContent>
 </xs:complexType>
</xs:schema>

<Items xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 <Item xsi:type="myType" len="5"/>
 <Item xsi:type="NOTmyType"/>
</Items>

Hope that helps,
George
---------------------------------------------------------------------
George Cristian Bina
<oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger
http://www.oxygenxml.com