Reference Sets Practical Guide

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The design of the ordered reference set supports three overall purposes:

  1. To specify a sequential order of a subset of components
  2. To specify prioritized groups within a subset of components 
  3. To define alternative hierarchies of components 

Ordering

Ordered reference set can also be used to create a simple ordered list of components, i.e. a list that do not include any nesting, or groups. For ordered lists that do not require grouping or hierarchical arrangement the value of linkedToId should be the digit zero (0), as this attribute becomes irrelevant.

This type of ordered reference set can for example be used to prioritize the sort order of the descriptions with identical terms when they are displayed. It can also be used to specify the order of descriptions displayed in a simple pick list.

Prioritization

Prioritization is similar to order but multiple components may have the same rank. In this case the value of the order attribute specify a priority order for a group of components. 

 

 

Alternative hierarchy

The diagram below Illustrates how the three attributes referencedComponentId, order and linkedToId are used to create an alternative hierarchical order of some of the concepts from the subtype hierarchy. 

Reference Set Specific Attributes

Specific reference set attributes used to build an alternative hierarchical view of SNOMED CT

Attribute

Description

referencedComponentId

The identifier of a SNOMED CT component that is included in the ordered list of alternative hierarchy.

order

Specifies the sort order of the list. The list is ordered by applying an ascending sort of the order value.
The value of order =1 represents the highest priority. A value of '0' is not allowed. Duplicate values are permitted and the sort order between two members with the same order value is not defined.
If the linkedToId value is not 0, sorting occurs within subgroups that share the same linkedToId value.

linkedToId

The identifier of a SNOMED CT component that acts as a grouper or hierarchy node, collecting together a subgroup from within the list.

This field either enables reference set member linked into a number of subgroups. These subgroups can be nested allowing representation of alternative hierarchies.

To link members into a subgroup, all components in the same subgroup should reference the same component. This can either be a component that represents the name of that subgroup or the first member of the subgroup. In the latter case, the first row of each subgroup will contain the same identifier in referencedComponentId and linkedToId and with order =1.

To link a number of children concepts to a single parent concept, one member record should exist per child, with the referencedComponentId field referencing the parent and this field referencing the child concept. The order field is then used to order the children concepts under the parent concept.

 See specification: 4.2.2. Ordered Reference Set

 

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