Value Set Revisions
A value set represents a list of concept codes from a single code system. Value sets are used to identify the list of possible values for a coded attribute based on the HL7 RIM.
Value sets can be constructed in one of three ways:
- A value set can represent all of the concept codes in a given code system
- A value set can represent selected codes from a code system. Codes may be selected by:
- Identifying individual concept codes
- Identifying a concept code and a relationship (e.g. hasSubtype, hasPart) and stating one of:
- The concept code and all related concepts are included in the set
- All related concepts except the named concept are included in the set
- All leaf nodes of the specified relationship are included in the set
- A value set can include codes from other value sets.
Note that the third form of construction actually makes it possible to mix concept codes from more than one code system in a single value set. This form should only be used, however, when the semantic space of the two value sets are disjoint - meaning that there is no possibility that the same concept could be represented using different codes from different systems.
When one value set is included in another set, sometimes it is useful to identify a concept code that represents the included value set as a whole (e.g. in the nullFlavor value set, one of the choices is “NoInformation (NI)”, which can be used instead of more specific flavors such as “masked (MSK)”, “not applicable (NA)”, etc.). When this is the case, the “whole” concept code can be identified by associating it with a value set as the “head code”. When this value set is included in a second value set, the include specifies whether the “head code” is a selectable value or not. Refer to the examples on the following pages for further clarification.
The value set revision process can be used to create new value sets as well as to modify the contents of existing sets.