Globally Unique Identifier - Subtypes

Subtypes

There are several flavors of GUIDs used in COM:

• IID – interface identifier; (The ones that are registered on a system are stored in the Windows Registry at the key HKEY_CLASSES_ROOT\Interface)
• CLSID – class identifier; (Stored in the registry at HKEY_CLASSES_ROOT\CLSID)
• LIBID – type library identifier;
• CATID – category identifier; (its presence on a class identifies it as belonging to certain class categories)

DCOM introduces many additional GUID subtypes:

• AppID – application identifier;
• MID – machine identifier;
• IPID – interface pointer identifier; (applicable to an interface engaged in RPC)
• CID – causality identifier; (applicable to a RPC session)
• OID – object identifier; (applicable to an object instance)
• OXID – object exporter identifier; (applicable to an instance of the system object that performs RPC)
• SETID – ping set identifier; (applicable to a group of objects)

These GUID subspaces may overlap, as the context of GUID usage defines its subtype. For example, there might be a class using the same GUID for its CLSID as another class is using for its IID — all without a problem. On the other hand, two classes using the same CLSID could not co-exist.