Object GUID
Each object (instance of a class) is also given a globally unique identifier (GUID). Unlike the Object ID, the GUID can be specified for an object when first created. If an object is not assigned a globally unique identifier at creation time, MDS will generate one for the object.When data versioning is enabled for a class, each version of an object in the class will have the same GUID.
A GUID is a Microsoft globally unique identifier and is a Microsoft implementation of the DCE UUID. All GUID values should be computer-generated to guarantee uniqueness. Microsoft provides function calls to create a GUID. (Executing the utility Guidgen.exe on Windows is one means to create GUIDs.)
An object can be retrieved by specifying the GUID of the object.