Implementing trading object services in COM

Identifying and locating services in distributed systems has always been problematic. Often, users have been obliged to identify not only the service required but also the specific supplier object type. Recently, the idea of trading services has been developed, allowing the developer to list a range of criteria required for a service, rather than an object type. We demonstrate how to employ Microsoft's Component Object Model (COM) categorizing facilities to implement a trading object service that allows for finer-grained matching criteria based on the semantics of types, subtypes and conformance. We conclude that, although categorization supports trading object services in COM, we are pushing COM to the limits of its capabilities. The static register/lookup nature of the COM registry restricts the trader from being realized as a truly dynamic discovery service.