A collection of collections; a subcollection of artifact type by function. Instances of device type by function are mutually unique with respect to the full set of primary functions that their instances perform. Examples include kitchen range and freezer. Counter-examples include electric range and upright freezer. There may be cases where two instances of device type by function (PROD1 and PROD2) are related by (generalization PROD1 PROD2); but this will only happen in cases where instances of PROD1 have some additional primary function(s) to those of PROD2. For example, the collections radio and clock radio are both instances of device type by function, and (generalization clock radio radio) is true.