MDAC 2.5 SDK - OLE DB Programmer's Reference
Chapter 7: BLOBs and COM Objects
COM objects can be stored in columns in a rowset. Such objects are required to expose IPersistStream, IPersistStreamInit, or IPersistStorage. The rowset has to know how to create instances of these objects, so it must store the objects' class IDs. How this is done is provider-specific.