Description logics in medical informatics

Description logics and related formalisms are being applied in at least five applications in medical informatics—terminology, intelligent user interfaces, decision support and semantic indexing, language technology, and systems integration. Important issues include size, complexity, connectivity, and the wide range of granularity required—medical terminologies require on the order of 250,000 concepts, some involving a dozen or more conjuncts with deep nesting; the nature of anatomy and physiology is that everything connects to everything else; and notions to be represented range from psychology to molecular biology. Technical issues for expressivity have focused on problems of part-whole relations and the need to provide “framelike” functionality—i.e., the ability to determine efficiently what can sensibly be said about any particular concept and means of handling at least limited cases of defaults with exceptions. There are also significant problems with “semantic normalisation” and “clinical pragmatics” because understanding medical notions often depends on implicit knowledge and some notions defy easy logical formulation. The two best known efforts—OpenGalen and SNOMED-RT—both use idiosyncratic description logics with generally limited expressivity but specialised extensions to cope with issues around part-whole and other transitive relations. There is also a conflict between the needs for re-use and the requirement for easy understandability by domain expert authors. OpenGalen has coped with this conflict by introducing a layered architecture with a high level “Intermediate Representation” which insulates authors from the details of the description logic which is treated as an “assembly language” rather than the primary medium for expressing the ontology.