The GALEN representation and integration language (GRAIL) has been developed to support effective clinical user interfaces and extensible re-usable models of medical terminology. It has been used successfully to develop the prototype GALEN common reference (CORE) model for medical terminology and for a series of projects in clinical user interfaces within the GALEN and PEN&PAD projects. GRAIL is a description logic or frame language with novel features to support part-whole and other transitive relations and to support the GALEN modelling style aimed at re-use and application independence. GRAIL began as an experimental language. However, it has clarified many requirements for an effective knowledge representation language for clinical concepts. It still has numerous limitations despite its practical successes. The GRAIL experience is expected to form the basis for future languages which meet the same requirements but have greater expressiveness and more soundly based semantics. This paper provides a description and motivation for the GRAIL language and gives examples of the modelling paradigm which it supports.

A common language, or terminology, for representing what clinicians have said and done is an important requirement for individual clinical systems, and it is a pre-requisite for integrating disparate applications in a distributed telematic healthcare environment. Formal representations based on description logics or closely related formalisms are increasingly used for representing medical terminologies. GALEN's experience in using one such formalism raises two major issues, as follows: how to make ontologies based on description logics easy to use and understand for both clinicians and applications developers; what features are required of the ontology and description logic if they are to achieve their aims. Based on our experience we put forward four contentions: two relating to each of these two issues, as follows: that natural language generation is essential to make a description logic based ontology accessible to users; that the description logic based ontology should be treated as an "assembly language" and accessed via "intermediate representations" oriented to users and "perspectives" adapting it to specific applications; that independence and reuse are best supported by partitioning the subsumption hierarchy of elementary concepts into orthogonal taxonomies, each of which forms a pure tree in which the branches at each level are disjoint but nonexhaustive subconcepts of the parent concept; that the expressivity of the description logic must include support for transitive relations despite the computational cost, and that this computational cost is acceptable in practice. The authors argue that these features will be necessary, though by no means sufficient, for the development of any large reusable ontology for medicine.

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