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A concept definition has one of the following two forms:

  1. A sufficiently defined concept is defined as a concept with a formal logic definition that is sufficient to distinguish its meaning from other similar concepts.

    Notes

    1. The meaning of SNOMED CT concept is expressed in a human-readable form by its Fully Specified Name(FSN) and has a formal logic definition represented by a set of defining relationships to other concepts. A Sufficiently defined concept has sufficient defining relationships to computably distinguish it from any concepts or expressions that are equivalent to or a subtype of the the defined concept.

    2. Contrast with  primitive concept.

    Examples

    The  concept 74400008 |appendicitis (disorder)| is sufficiently defined by the following definition because any concept for which these defining relationships are true are either the disorder "appendicitis" or a subtype of "appendicitis".

    Table 1:  Definition of: 74400008|appendicitis (disorder)| - (sufficiently defined)

    •  The value of a sufficient definition is that it allows a postcoordinated expression that is sufficient to define a concept to be recognized as equivalent to (or a subtype of) a defined concept.

  2. A primitive concept is defined as a concept with a formal logic definition that is not sufficient to distinguish its meaning from other similar concepts.

    Note

    1. The meaning of SNOMED CT concept is expressed in a human-readable form by its Fully Specified Name.

    2. Each concept also has a formal logic definition represented by a set of defining relationships to other concepts. This logic definition is computer processable. A primitive concept does not have sufficient defining relationships to computably distinguish them from more general concepts(supertypes).

    3. See also sufficiently defined concept.

    Example

    The concept 5596004 |atypical appendicitis (disorder)| is primitive because the following definition is not sufficient to distinguish "atypical appendicitis" from any other type of "appendicitis".

    Table 1: Definition of 5596004|atypical appendicitis (disorder)| - (primitive)

Necessary Conditions

All SNOMED CT defining relationships currently released are necessarily (always) true for the concept defined. Relationships that are necessarily true are also know as necessary conditions.

A necessary condition is defined as a characteristic that is always true of a concept.

Example

Sufficient Sets of Conditions

In practice there can be several sufficient definitions for a concept. That is to say several different ways in which a concept could be sufficiently defined by different sets of defining relationships For example:

Gastric ulcer is defined as follows:

This is a sufficient definition because any 56208002 |ulcer| in a 69695003 |stomach structure| is by definition a 397825006 |gastric ulcer| . Based on this definition:

Any postcoordinated expression that specified a disease involving an 56208002 |ulcer| with 363698007 |finding site| 69695003 |stomach structure| would be equivalent to or a subtype of 397825006 |gastric ulcer| 

However, a query for all disorders involving 78653002 |gastric mucosa| would incorrectly exclude 397825006 |gastric ulcer| as the site is specified as 78653002 |gastric mucosa| which is more specific than 69695003 |stomach structure| . In reality there is another sufficient set defining relationships

but this is not currently represented in SNOMED CT. The reason for this is that the currently the profile of description logic used by SNOMED CT does not support representation of multiple sufficient sets. 

When multiple sufficient sets are supported, satisfying a single sufficient set enables an inference to be made that all necessary conditions must also be true. For example

 

However, as the current profile does not enable recognition of multiple sufficient sets, the general rule is to represent the most general sufficient set as this gives the greatest coverage for subsumption testing. This approach is taken because including more defining relationships, without distinguishing them from the sufficient set means some logically equivalent expressions will not compute as equivalent to or subsumed by the defined concept. This occurs in any cases where the expression does not include one of the attributes in the definition - even if it was not part of the logically sufficient set.


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