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A set of textual descriptions are assigned to every concept. These provide the human readable form of a concept. Two types of description are used to represent every concept - Fully Specified Name (FSN) and Synonym.

The FSN represents a unique, unambiguous description of a concept's meaning. The FSN is not intended to be displayed in clinical records, but is instead used to disambiguate the distinct meaning of each different concept. This is particularly useful when different concepts are referred to by the same commonly used word or phrase. Each concept can have only one FSN in each language or dialect.

A represents a term that can be used to display or select a . A concept may have several synonyms. This allows users of SNOMED CT to use the terms they prefer to refer to a specific clinical meaning. Concepts can have multiple synonyms, and the associated terms are not necessarily unique – thus two concepts can have the same synonym term. Interpretation of a synonymous term therefore depends on the concept identifier.

Each concept has one synonym which is marked as |preferred | in a given language, dialect, or context of use. This is known as the "preferred term" and is a word or phrase commonly used by clinicians to name that concept. In each language, dialect or context of use, one and only one synonym can be marked as | preferred |. Any number of other synonyms that are valid in a language, dialect or context of use can be marked as | acceptable |.

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The |is a| relationships form the hierarchies of SNOMED CT. They are therefore also known as hierarchical relationships. The source concept of the |is a| relationship has a more specific clinical meaning than the target concept. This means that the level of clinical detail of the concepts increases with the depth of the hierarchies.

If two concepts are directly linked by a single |is a| relationship, the source concept is said to be a "subtype child" of the destination concept. The destination concept is referred to as a "supertype parent". Any concept that is the source of a sequence of one or more |is a| relationships leading to a specified destination concept, is a "subtype descendant" of that concept. Similarly, any concept that is the destination of a sequence of one or more |is a| relationships leading to a specified source concept, is a "supertype ancestor" of that concept. It is also said that the source concept of an |is a| relationship "is subsumed by" the target concept, and that the target concept of an |is a| relationship "subsumes" the source concept.

Each concept can have |is a| relationships to several other concepts (i.e. a concept may have multiple supertype parent concepts). As a result the SNOMED CT hierarchy is not a simple tree but has a structure that is known as a "polyhierarchy".

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An attribute relationship contributes to the definition of the source concept by associating it with the value of a defining characteristic. The characteristic (attribute) is specified by the relationship type and the value is provided by the destination of the relationship.

The following example shows the defining relationships of the concept |abscess of heart|. The attribute relationships |associated morphology| and |finding site| are used to associate the source concept |abscess of heart| to respectively the target concepts |abscess|, and |heart structure|.

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Unlike |is a| relationships, which are used to define all concepts, the applicability of each type of attribute relationship is limited to a defined domain and range. The domain refers to the concepts that can serve as source concepts for that type of attribute relationship. The range refers to the concepts that can serve as destinations (values) for those attributes. The domain and range specification ensure consistent definitions that can be used to infer additional semantic relationships to deliver reliable meaning-based retrieval of the composed meanings.

The first example below violates the domain constraint of |causative agent|, as descendants of |body structure| are not in the domain of |causative agent|. The second example below is valid with respect to the domain constraint of |causative agent|, because |disorder| is in the domain of |causative agent|. However, this example violates the range constraint of |causative agent|, as descendants of morphological abnormality are not in the range of |causative agent|.

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In SNOMED CT every concept is specified as either fully defined or primitive.

A is fully-defined if its are sufficient to distinguish its meaning from other similar concepts. One example is that the |acute disease| is fully-defined by its two defining . The first  is |is a||disease| and the second is |clinical course||sudden onset AND/OR short duration|. Stating that this concept is fully-defined means that any concept that |is a||disease| and has a |clinical course| of |sudden onset AND/OR short duration| is a subtype of this concept (or the concept itself).

A is (not fully-defined) if its are not sufficient to uniquely distinguish its meaning from other similar concepts. One example is that the |disease| and |drug action| share the same : namely a of type |is a| to the |clinical finding|. This is despite the fact that the |disease| and |drug action| represent different clinical ideas.

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