A collection of collections; a subcollection of kind of artifact not distinguished by brand or model. Instances of artifact type by function are mutually unique with respect to the full set of the primary intended uses of their instances. Examples include dessert and sofa. Counter-examples include fountain pen (which has the same primary function as its genls, pen) and piece of furniture (specs of which have different primary uses). There may be cases where two instances of artifact 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 sofa and hide-a-beds are both instances of artifact type by function, and (generalization hide-a-beds sofa) is true.