Aliases: [ Collection, Collections, Form, Forms, Kind, Kind of thing, Kind of things, Kinds, Kinds of thing, Kinds of things, Sort, Sorts, Type, Type of things, Types, Types of thing, Types of things ]
A specialization of intensional or extensional set (q.v.). This is the collection of all collections of things. Each type of thing is a kind or type of thing whose instances share a certain property, attribute, or feature. For example, cat is the collection of all and only cats, and binary function is the collection of all and only functions taking two arguments.
The notion of collection is fundamental to the Cyc ontology, and is thus difficult to define in a precise and substantive way. But it is instructive to compare it to the mathematical notion of a set (see set). Like a set, a collection is an abstract thing (i.e. aspatial and atemporal) that is not an individual (cf.), but instead has elements (see Element Of). Unlike a set, however, the elements or instances (see Isa) of a given collection can vary from context to context, and it is possible for distinct collections to have exactly the same elements (i.e. to have the same Extent) with respect to a given context. For example, the (non-reified) collections Chordate and Renate are co-extensional in the context of the present-day actual world, but have differring extents with respect to hypothetical contexts in which there exist creatures having hearts but not kidneys. This difference is sometimes summarized by saying that sets are extensional things and collections are intensional things.
Many, though by no means all, of the collections reified in the Cyc ontology correspond to natural kinds or classes. It is particulary useful to reify collections that are difficult to define precisely, but about which there are many common-sense rules and other things to state. For example, it would not be worthwile to introduce a constant 'WhiteCat', both because it's easy to define the collection of white cats in terms of more general, already-reified notions (e.g. '(Collection Intersection 2 Fncatwhite)'), and because there's not much to say about that particular collection. white collar worker, on the other hand, is a good collection to have reified, as it is hard to define precisely, yet is a collection about which there are many things to say.
The notion of collection is fundamental to the Cyc ontology, and is thus difficult to define in a precise and substantive way. But it is instructive to compare it to the mathematical notion of a set (see set). Like a set, a collection is an abstract thing (i.e. aspatial and atemporal) that is not an individual (cf.), but instead has elements (see Element Of). Unlike a set, however, the elements or instances (see Isa) of a given collection can vary from context to context, and it is possible for distinct collections to have exactly the same elements (i.e. to have the same Extent) with respect to a given context. For example, the (non-reified) collections Chordate and Renate are co-extensional in the context of the present-day actual world, but have differring extents with respect to hypothetical contexts in which there exist creatures having hearts but not kidneys. This difference is sometimes summarized by saying that sets are extensional things and collections are intensional things.
Many, though by no means all, of the collections reified in the Cyc ontology correspond to natural kinds or classes. It is particulary useful to reify collections that are difficult to define precisely, but about which there are many common-sense rules and other things to state. For example, it would not be worthwile to introduce a constant 'WhiteCat', both because it's easy to define the collection of white cats in terms of more general, already-reified notions (e.g. '(Collection Intersection 2 Fn cat white)'), and because there's not much to say about that particular collection. white collar worker, on the other hand, is a good collection to have reified, as it is hard to define precisely, yet is a collection about which there are many things to say.
Some of the many reified specializations of type of thing are first-order Cyc collection, time dependent collection, and type of object.