Situation
Value sets expression for the NCI Thesaurus (NCIt) has scaled up over the last few years. The LexEVS implementation model of loading Value Set Definitions and their Resolved Value Set Coding Scheme counterparts has become unwieldy as the number of value sets has grown.
Background
Originally values sets for LexEVS were expressed in terms similar to the ISO 11179 specification. Value domains were conceived as a set of rules that could be applied to any version of a given terminology with the expectation that a current version of the value set would be expressed. Eventually the NCIt provided a framework of relations to define value sets in a more succinct set of rules. This framework was eventually pointed to as a more viable method for defining value sets and it was suggested as an alternative source to a set of nearly a thousand xml files that represented the value set definitions.
Assessment
Value sets asserted by the terminology source (Source Asserted Value Sets), provide a complete definition of value sets in static terms It does not require resolving a graph, or a union of a variety of sources to achieve its definition. At the same time the root (or target) entity of the asserted values carries adequate metadata to define what former resolved value set coding scheme represented without the workflow complexity of having to create separate coding scheme database entries. This resulted in higher performing value set retrieval and eliminated very lengthy loading times.
Recommendation
