Approach to Value Set Constraint Specifications
The value set specifications are presented as tables in the following general structure:
|Class Name: The Clinical Statement pattern class is identified here
||Class Code: If relevant, distinct classCodes are identified here
|Attribute Name: The relevant attribute(s) is/are identified here
|Narrative description of vocabulary domain:|
The relevant narrative description of the vocabulary domain is identified here.
|Value set representation:|
Value sets are identified here, using the SNOMED CT compositional grammar extended for the purpose of this Implementation
Guide as described in Appendix B/>.
Any notes relevant to this className+classCode+attributeName value set specification are made here.
Specifications of the "simple" form provided in this section have some limitations but they serve two important purposes described in the following sub-sections.
A large clinical terminology, such as SNOMED CT, represents a number of lexically similar concepts which are grammatically, linguistically or semantically distinct. This phenomenon is particularly pronounced if the terminology is considered without any kind of partitioning. The coarse-grained partitioning specified by these constraints simplifies and clarifies decisions about which of a set of superficially similar SNOMED CT concepts are appropriate to particular HL7 vocabulary domains.
For example, consider a vocabulary domain specification that is intended to represent "an adverse event in reaction to a drug". The simple value set constraints in this specifications exclude these inappropriate alternatives and thus provided a helpful guide for value set developers.
- The most suitable SNOMED CT concepts to represent such an event would be those subsumed by [ <<62014003 | adverse reaction to drug ].
- However from a lexical perspective other less appropriate concepts may appear to be suitable. For example
- The reference to "adverse drugs reaction" may suggest use of subtypes of the procedure concept [ <<396079007 | assessment of adverse drug reactions ].
- The reference to "drug" may suggest concepts in the use of subtypes of [ <<373873005 | pharmaceutical / biologic product ] or [ <<410942007 | drug or medicament ].
The Schematic Illustrations of SNOMED CT Expressions identify the "clinical kernel" or primary clinical "focus concept" that may exist alone or as part of a contextualized expression. In most cases, the simple value set constraints in this specification apply to this clinical focus concept. In combination with the SNOMED CT concept model these constraints form a foundation for more detailed "complete" value set specifications (as explored in Detailed aspects of issues with a vocabulary specification formalism).
Simple value set constraints can be regarded as a set of subsumption clauses related by OR logic. Each clause permits the inclusion of a focus concept that is subsumed by a specified concept. In contrast, a more complete specification would check normal form transformations of candidate expressions against a variety of subsumption and role-based restrictions. In addition a complete specification require support of a full set of logical operators between clauses (i.e. OR, AND, NOT).
For example, consider a value-set constraint which indicates that the "focus concept" must be a kind of [ <<404684003 | clinical finding ].
- The concept model indicates that a [ 404684003 | clinical finding ] concept
- can be refined by name/value pairs with attribute names such as [ 363698007 | finding site ], [ 246112005 | severity ], [ 116676008 | associated morphology ] etc.,
- can be the value to the attribute name [ 246090004 | associated finding ]
- as part of the definition or refinement of a [ 413350009 | finding with explicit context ]
- as part of post-coordinated expression that includes the [ 404684003 | clinical finding ] within a context wrapper.
- A comprehensive notation for value sets that allow subtypes of [ 404684003 | clinical finding ] may therefore also need to indicate whether any limitations apply either to the refinement or situation in which the concepts are used.
- The context wrapper may, for instance, be used to communicate negation and uncertainty and may thus be required to support some types of information. However, it may also be necessary to constrain the use of context in a manner that is relevant to the Act.moodCode or other attributes and association in the HL7 representation.