Guid Simple Type 

Defines the type of values used to identify objects with a GUID value.

<xs:simpleType name="Guid">
    <xs:restriction
        base="string"
    >
        <xs:pattern
            value="[0-9a-fA-F]{8-[0-9a-fA-F]{4-[0-9a-fA-F]{4-[0-9a-fA-F]{4-[0-9a-fA-F]{12"
         />
    </xs:restriction>
</xs:simpleType>

Patterns

The following pattern is defined by the Guid simple type:

[0-9a-fA-F]{8-[0-9a-fA-F]{4-[0-9a-fA-F]{4-[0-9a-fA-F]{4-[0-9a-fA-F]{12

A string that is a GUID value, which is a unique 128-bit number. For example, 5b2fc63a-8af4-44cb-960c-aefdced908d6.