DPWS is lacking a description mechanism and language to describe the relationship between a device type and the hosted services hosted by a device implementing this type. For instance, a printer conformant to a standardized printer type should always expose the same set of mandatory hosted services, plus maybe a set of standard and non-standard optional hosted services. There is no standard language (similar in purpose to the abstract part of WSDL) to describe this relationship. WSDL itself does not seem applicable to a device. Today, the solution is to rely on out-of-band information to establish the link between an interface exposed by a hosted service (e.g. a PrintService interface/port type) and the device type that must be used in the Probe request to retrieve the appropriate device hosting the hosted service.