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 pre- and 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 post- coordination 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.