To programmatically discover and interact with services in ubiquitous computing environments, an application needs to solve two problems: (1) is it semantically meanngful to interact with a service? If the task is "printing a file", a printer service would be appropriate, but a screen rendering service or CD player service would not. (2) If yes, what are the mechanics of interacting with the service — remote invocation mechanics, names of methods, numbers and types of arguments, etc.? Existing service frameworks such as Jini [1] and UPnP [22] conflate these problems — two services are "semantically compatible" if and only if their interface signatures match. As a result, interoperability is severely restricted unless there is a single, globally agreed-upon, unique interface for each service type. By separating the two subproblems and delegating different parts of the problem to the user and the system, we show how applications can interoperate with services even when globally unique interfaces do not exist for certain services.