Current Version - Under Revision
The use and representation of hierarchies in SNOMED CT differs from the approach taken in many older code systems and classifications. This has a number of consequences that may affect the migration of queries, decision support protocols and data entry templates.
SNOMED International , all 'diagnoses related to the digestive system' can be retrieved by a query for
all codes starting with 'D5'
The Identifier of a SNOMED CT concept does not provide any information about the way it relates to other concepts . Therefore, a simple pattern matching query cannot be used to retrieve related information represented using SNOMED CT . Instead, the query that specifies a subtype of the required concept is evaluated by testing the transitive closure of the set of subtype Relationships .
Example: All 'diagnoses related to the digestive system' can be retrieved by a query for expressions that are subtypes of 119292006 |disorder of gastrointestinal tract| .
Example: All 'diagnoses related to the digestive system' is some schemes may exclude codes that are primarily classified as infective disorders even they affect the digestive system. However, a SNOMED CT query includes all subtype concepts regardless of whether they are also in another hierarchy.
Example: Should a query for the concept 'nephrectomy' return only patients who have had a total nephrectomy or should the results include those with a record of a partial nephrectomy? If the partial nephrectomies are to be included then how much kidney tissue must be removed to count as a nephrectomy? If the partial nephrectomies are not included then should a record entry including the concept 'nephrectomy' (without specifying partial or total) be included? The SNOMED CT subtype hierarchy determines the answer to these questions based on the defining Relationships . The query may need to be refined to meet more specific expectations.