SNOMED CT includes 19 domains arranged in a polyhierarchical structure. Each hierarchy is an ordered organization of concepts linked together through IS A relationships. Each concept may have one or more parents.
The hierarchical arrangement is helpful for locating concepts, grouping similar concepts, and conveying meaning. For example, if we see the concept cell under the concept anatomic entity we will understand the intended meaning as different than if it appeared under the concepts room or power source (Desiderata for Controlled Medical Vocabularies in the Twenty-First Century by J.J. Cimino published in Methods of Information in Medicine 1998:37:394-403).
Concepts are linked to their more general parent concept codes directly above them in a hierarchy. Concepts with more general meanings are usually presented as being at the top of the hierarchy and then at each level down the hierarchy, the meanings become increasingly more specific or specialized.
The domains contain all of the components (clinical, administrative, database structure, as well as other components that express how the domains relate to each other) necessary to create SNOMED CT concepts and maintain the database structure.
A domain is a set of concepts which the Concept Model permits to be defined or refined, using a particular set of attributes and ranges
Some domains do not have attributes and ranges but may if a concept model is created
A domain, to which an attribute can be applied, is typically defined to include concepts in one or more branches of the subtype hierarchy
The domain of 116676008 | Associated morphology (attribute)| is defined as subtype of 404684003 | Clinical finding (finding)|
The range of values of 116676008 | Associated morphology (attribute)| is subtypes of 49755003 | Morphologically abnormal structure (morphologic abnormality)|
The following table lists the domains, definitions, and examples. *Those without a concept model are marked with an asterisk.
|Domain/Top-level Hierarchy (alpha-sorted)||Examples|
|3||Environment and Geographical Location*|
|13||Situation with Explicit Context|
|14||SNOMED CT Model Component*|
|18||Staging and Scales*|
The scale, or level of detail, in a terminology is called granularity. Concepts and meanings range from very general, or coarse, to very specific, or fine. SNOMED CT has multiple granularities, which is an important component of terminologies that are multipurpose. The broader meanings are useful for aggregation (e.g. Clinical finding, Procedure, etc.), but are not intended for recording individual patient data.
The progressive levels of refinement are used to meet clinical data requirements. There are, however, limits to the degree of precoordination of certain types of complex statements.
In general, concepts in SNOMED CT should name things that exist in the real world. The concepts are usually names or short noun phrases, not complete sentences or paragraphs.
SNOMED CT is intended to be used with electronic health applications that can support full clinical statements, along with their attributions, dates, times, and statement interrelationships. It may be challenging to balance SNOMED CT content with the needs of those using electronic health applications. For example, some older applications may require concepts outside of the scope of SNOMED CT. SNOMED CT tries to maximize its usefulness and at the same time minimize precoordination.