16. The method of claim 15 , wherein, for each group description in said merged set, the method further comprising: creating a derived instance for each group member included in said each group description, said derived instance being a derived data element instance if said each group member is a data element, said derived instance being a derived data element group instance if said group member is a data element group.
16. The method of claim 15 , wherein, for each group description in said merged set, the method further comprising: creating a derived instance for each group member included in said each group description, said derived instance being a derived data element instance if said each group member is a data element, said derived instance being a derived data element group instance if said group member is a data element group. 17. The method of claim 16 , wherein a property specified for each group member indicates placement of said group member in a one of a predetermined number of buckets, said predetermined number of buckets determining a relative ordering of said each group member with respect to other group members.