Essential SNOMED: Simplifying SNOMED-CT and supporting Integration with Health Information Models

SNOMED CT (SCT) has been designed and implemented in an era when health computer systems generally required terminology representations in the form of singular precoordinated concepts. Consequently, much of SCT content represents pre-coordinated concepts and their relationships. In this conceptual paper the role of preand post-coordinated terminology expressions are considered in the context of the current development direction of Electronic Health Records and the use of communications and knowledge repositories. The move from current SCT structures to an implementation form of SCT that focuses on “atomic concepts” will support post-coordination and terminology binding to information models. This core or “essential” SNOMED CT called SNOMED Essential Terminology (S-ET) would be smaller in terms of core concept numbers, simpler, easier to maintain and more intuitive for implementers. Our proposed implementation form of SNOMED CT would contain only “atomic concepts” with their attendant hierarchies and relationship data. These would be supported by a strict model for representing current and future pre-coordinated concepts based on the use of an existing specific postcoordination expression, grammar, or representation. The resulting concept expressions would be postcoordinated from a smaller core of atomic components. Using definitional relationships, the proposed implementation form could equate existing pre-coordinated terms with postcoordinated representations, allowing SCT to maintain links with legacy data. A strategy for testing and implementing this approach is discussed and empirical research and feasibility testing is recommended. INTRODUCTION SNOMED CT (SCT) is becoming the international standard clinical terminology with a new international licensing and governance process which makes it widely accessible. The adoption of SCT by multiple countries was influenced by many published studies demonstrating its comprehensive coverage [1-4] and advanced structural features. SNOMED CT has antecedents in the College of American Pathologists family of terminologies, the UK National Health Service Read Codes. As with any living language, it has absorbed content from a number of other terminologies and classifications. SCT contains concepts and terms that describe the “language of use” as well as concepts which define the “language of meaning”[5-7]. Consequently, SCT contains many pre-coordinated concepts that have varying levels of semantic complexity alongside the component or essential concepts which are themselves the building blocks of these complex clinical expressions. While there are sound historical and ongoing pragmatic reasons for this evolutionary development, the resulting mix of concept structures makes implementation within various information models complex and prone to variation. Currently, SCT is “cluttered” with precoordinated terms that are incompletely defined by the internal information model that exists within SCT, making transformations between existing precoordinated terms and postcoordinated representations difficult to achieve. This result limits opportunities for interoperability across systems, [8] which is one of the key objectives of a controlled terminology. This conceptual paper brings to notice issues that Representing and sharing knowledge using SNOMED Proceedings of the 3rd international conference on Knowledge Representation in Medicine (KR-MED 2008) R. Cornet, K.A. Spackman (Eds)