The   field will initially be set to to keep compatibility with the release. Widening the range of this field to include other values (such as |All|) will in future increase the expressive power of However, this is likely to come at the cost of an increase in reasoning complexity, leading to potential issues for classification tooling.

Notes: 

1. The modiferId field has been included at this stage as the format is likely to be stable for at least a five year period, without addition or deletion of fields. Within that period it is anticipated that other   values will be added. Therefore, although not fully implemented at this stage, this field has been included in the initial RF2 specification as it represents an integral part of the used by

2. Any expansion of to include with a   set to a value other than will be discussed with prior to introduction.

3. Changes have been made to the "Immutability" values shown in the above table in the 2014-07-31 version. These changes reflect the fact that the values in the following columns of a uniquely identified relationship have occurred in historical data and in these cases tracking the history of these changes is of greater value that insisting on immutability. 

   • relationshipGroup: The number can change though the logical content of the group represented should not change. Additionally no significance should be read into the relationshipGroup value of an inactive

   • characteristicType: This has changed in historical data but should not change in future;
   • modifierId: Since there is currently only one value for this no changes are possible but if the permitted values are extended as suggested above then it is likely that changes would be required.