The |reference set descriptor reference set|  is a reference set used to specify the format of all reference sets included in a release. The data type and meaning of the referenced component and each additional field within each reference set is described by this reference set. More specifically, the reference set descriptor is used to define:

1. The order of appearance of additional attributes (other than those mandatory for all reference sets). The AttributeOrder attribute
2. The name and purpose of the additional attributes. The attributeDescription attribute
3. The data types for the additional attributes. The attributeType attribute

The table below shows an excerpt from the Reference Set Descriptor, to illustrate how the attributes of the predefined reference set types are specified consistently.

Specializing a Descriptor Template

When a newis created in anit must (by default) conform to the reference set descriptors of its closest supertype (if one exists). Creation of a description template for a newis optional in an extension, if the reference set has a supertype which itself has a descriptor template.

However, it is possible for ato specialize the descriptor template of its supertype, by creating a copy and replacing the |Attribute description| or |Attribute type| values with a subtype.

For example, if ahas a descriptor, in which the |Attribute description| = |Referenced component| and the |Attribute type| = |Component type| , then thesubtype may replace this descriptor with one in which the |Attribute description| = |Component type| and the |Attribute type| = |Concept type component| (since |Concept type component| is a subtype of |Component type| ). In this way, thedescriptors may be specialized for use by the subtypes of the.