By constructing local extensions to SNOMED we aim to enrich existing medical and related data stores, simplify the expression of complex queries, and establish a foundation for semantic integration of data from multiple sources. Specifically, a local extension can be constructed from the controlled vocabulary(ies) used in the medical data. In combination with SNOMED, this local extension makes explicit the implicit semantics of the terms in the controlled vocabulary. By using SNOMED as a base ontology we can exploit the existing knowledge encoded in it and simplify the task of reifying the implicit semantics of the controlled vocabulary. Queries can now be formulated using the relationships encoded in the extended SNOMED rather than embedding them ad-hoc into the query itself. Additionally, SNOMED can then act as a common point of integration, providing a shared set of concepts for querying across multiple data sets. Key to practical construction of a local extension to SNOMED is appr...