2.2.5.8 guid

msdn link

Namespace: http://schemas.microsoft.com/2003/10/Serialization/

The guid simple type represents a GUID.

 <xs:simpleType name="guid" xmlns:xs="http://www.w3.org/2001/XMLSchema">
   <xs:restriction base="xs:string">
     <xs:pattern value="[\da-fA-F]{8}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{4}-[\da-fA-F]{12}"/>
   </xs:restriction>
 </xs:simpleType>