We present a novel approach to describe and reason about stateless information processing services. It can be seen as an extension of standard descriptions which makes explicit the relationship between inputs and outputs and takes into account OWL ontologies to fix the meaning of the terms used in a service description. This allows us to define a notion of matching between services which yields high precision and recall for service location. We explain why matching is decidable, and provide biomedical example services to illustrate the utility of our approach.