Date Format in XSD Schema

Helo All

Can anybobdy help me in specifying date format in xsd.  I want to restrict 
date format in dd/mm/ccyy format, and also want to make this date optional.  
At the moment I am doing this

<xs:element name="DateAdded">
    <xs:simpleType>
	<xs:restriction base="xs:string">
	      <xs:pattern value="[0-2][0-9][/][0-1][0-9][/][0-2][0-2][0-9][0-9]"/>
	</xs:restriction>
    </xs:simpleType>
</xs:element>

I want to make this value optional.

Also how to specify an email address in xsd and make it optional.

Thnaks

Khurram.

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