2.2.2.2 XID Structure

An XID structure contains an external identifier for an entity within a message store.


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NamespaceGuid

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LocalId (variable)

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NamespaceGuid (16 bytes):  A 128-bit GUID. This field identifies the namespace of the LocalId field.

LocalId (variable):  A variable binary value. This field contains the ID of the entity in the namespace specified by the NamespaceGuid field. This field has a minimum length of 1 byte and a maximum length of 8 bytes.

For more details about GID structures, which are a subtype of an XID structure, see [MS-OXCDATA] section 2.2.1.3. For GIDs, the DatabaseGuid field maps to the NamespaceGuid field, and the GlobalCounter field maps to the LocalId field.

All XID structures that have the same value for their NamespaceGuid fields MUST have LocalId fields of the same length. However, the size of the value specified by the LocalId field cannot be determined by examining the value of the NamespaceGuid field and MUST be provided externally. In most cases, XIDs are present within other structures that specify information about the size of the XID, such as the SizedXid structure, as specified in section 2.2.2.3.1, or the propValue element, as specified in section 2.2.4.3.21.