XSD validation.

Question

What is the best way to write mandatory field validation in XSD?

i am trying below code but it is not working.

 

<xs:element name="DOB">

<xs:complexType>

<xs:simpleContent>

<xs:extension base="xs:string">

<xs:attribute name="DOB" type="xs:string" use="required" />

</xs:extension>

</xs:simpleContent>

</xs:complexType>

</xs:element>