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Ordered association reference sets can be used to specify and display a customized navigation hierarchy. Alternative hierarchical representations of SNOMED CT can support data entry by satisfying the requirements of a specific use case, and addressing some of the challenges of displaying an unordered polyhierarchy (as defined by SNOMED CT's subtype structure).

The figure below shows the way a navigation hierarchy is represented. The example reference set contains a set of description components used to describe finger structures. 

The | All fingers | components is linked to the | Hand |, and the | Thumb | is linked to the | All fingers component | The | Thumb | is placed first because it has the order value 1. Similarly, the components for | Second finger |, | Third finger |, | Fourth finger | and | Fifth finger | are also linked to the | All finger | component in the order specified by the order value. As shown in the figure the direction of the associations goes from the referenceComponentId to the linkedToId, so the components referenced by the linkedToId are used to form the groups specified in the hierarchy

id

effective Time

active

moduleId

refsetId

refsetId_term

referencedComponentId

referencedComponentId_term

targetComponentId

targetComponentId_term

order

20160731

1

19999999103

159999999105

Associations as ordered reference set

70327001

All fingers

141819019

Hand

1

20160731

1

19999999103

159999999105

Associations as ordered reference set

127053016

Thumb

70327001

All fingers

1

20160731

1

19999999103

159999999105

Associations as ordered reference set

138873019

Second finger

70327001

All fingers

2

20160731

1

19999999103

159999999105

Associations as ordered reference set

108884010

Third finger

70327001

All fingers

3

20160731

1

19999999103

159999999105

Associations as ordered reference set

136021011

Fourth finger

70327001

All fingers

4

20160731

1

19999999103

159999999105

Associations as ordered reference set

21356012

Fifth finger

70327001

All fingers

5

 


Figure 3.2.1.5-1: Navigation hierarchy example.


The usability of the ordered association reference set for representing alternative hierarchy can be maximized by:

  • Constraining the number of levels in the hierarchy and/or the number of concepts at each level.
    • Using many levels, each with a relatively small number of concepts, allows the most common options to be displayed with a higher priority.
    • Using fewer levels, each with a relatively large number of concepts can reduce the number of levels that needs to be navigated to find an appropriate concept.
    • Options that are never (or rarely) used can be excluded from a customized navigation hierarchy to limit the range of choices available.
  • Ordering each concept at the same hierarchical level, to match user preferences or to facilitate faster access to more frequently used options.
  • Ensuring that the navigation hierarchy is adapted to meet the requirements of a specific use case, without affecting the correctness of the subtype hierarchy (and associated logical inferences).

 


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