XSD Constraints

[Steve Fletcher]

Hello,

I'm writing a schema, and I want to apply some contraints to the
combination of values that can be supplied for the attributes for one
of the elements. The problem concerns the Operation element in the xml
fragment below. The element has two attrbiutes, and I want to apply
some rules that ensure that the values provided are in agreement with
one another. For example, I want ensure the CREATE, UPDATE and DELETE
values for the Operation attribute are provided with a Sequence
number, but that the CREATEUPDATE value of Operation attribute is not
have a Sequence Number provided.

I want to <b>allow</bonly the following combinations:
<ns1:Operation Operation='CREATE' Sequence=(any +ve int)/>
<ns1:Data>Data</ns1:Data>
....
<ns1:Operation Operation="UDPATE' Sequence=(any +ve int)/>
<ns1:Data>Data</ns1:Data>
....
<ns1:Operation Oprtation='DELETE' Sequence=(any +ve int)/>
<ns1:Data>Data</ns1:Data>
....
<ns1:Operation Operation='CREATEUPDATE'/>
<ns1:Data>Data</ns1:Data>

but <b>prevent<b/the following xml
<ns1:Operation Operation='CREATEUPDATE' Sequence=(any +ve int)/>
<ns1:Data>Data</ns1:Data>
Does anyone know how this is achieved?
--Fragment--
<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns="http://www.world.com" xmlns:xs="http://www.w3.org/
2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata"
xmlns:ns1="http://world.com/schema.xsd" targetNamespace="http://
world.com/schema.xsd" elementFormDefault="qualified" version="1.5">
<xs:element name="ScriptMark" type="ns1:MarkType"/>
<xs:complexType name="MarkType">
<xs:sequence>
<xs:element name="Operation" type="ns1:OperationType"/>
<xs:element name="Data" type="xs:string" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="OperationType">
<xs:attribute name="Operation" type="ns1:OpType" use="required"/>
<xs:attribute name="Sequence" type="ns1:SequenceType" use="optional"/

>

</xs:complexType>
<xs:simpleType name="OpType">
<xs:restriction base="xs:string">
<xs:enumeration value="CREATEUPDATE"/>
<xs:enumeration value="CREATE"/>
<xs:enumeration value="UPDATE"/>
<xs:enumeration value="DELETE"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="SequenceType">
<xs:restriction base="xs:int">
<xs:minInclusive value="0"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>