]> 2008/06/10 OpenCyc Knowledge Base Copyright© 2001-2008 Cycorp, Inc., http://www.cyc.com/, Austin, TX, USA This file contains an OWL representation of information contained in the OpenCyc Knowledge Base. The content of this OWL file is licensed under the Creative Commons Attribution 3.0 license whose text can be found at http://creativecommons.org/licenses/by/3.0/legalcode. The content of this OWL file, including the OpenCyc content it represents, constitutes the "Work" referred to in the Creative Commons license. The terms of this license equally apply to, without limitation, renamings and other logically equivalent reformulations of the content of this OWL file (or portions thereof) in any natural or formal language, as well as to derivations of this content or inclusion of it in other ontologies. externalID A unique, language-neutral, variable-sized identifier for a concept that can be used to refer unambiguously to that concept across OWL exports or across Cyc inference engines. label A natural-language representation for a concept that is both human readable and readable by the Cyc inference engine. These terms are not guaranteed to refer to the same concept across time but are guaranteed to be consistent within a particular OWL export. Use 'cycAnnot:externalID' for unambiguously referring to a concept across OWL exports or across Cyc inference engines. A collection of collections. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> is a collection whose membership changes over time. For example, (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX35wpEbGdrcN5Y29ycA" class="cyc_term">LiquidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) is a time dependent collection. A given portion of water might be an instance of (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX35wpEbGdrcN5Y29ycA" class="cyc_term">LiquidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) in the summer, and an instance of the disjoint collection (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX0JwpEbGdrcN5Y29ycA" class="cyc_term">SolidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) in the winter. In contrast, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVieEpwpEbGdrcN5Y29ycA" class="cyc_term">Integer</a> is a <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvzndCZwpEbGdrcN5Y29ycA" class="cyc_term">TimeIndependentCollection</a> (q.v.) because the collection of integers does not change its membership over time. time dependent collection TimeDependentCollection ExistenceDependentCollection A specialization of both <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> and <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rHIBS0h_TEdaAAABQ2rksLw" class="cyc_term">FirstOrderCollection</a> (qq.v.). This is the collection of all first-order collections of which something can be an instance only while that thing exists. Note that a given instance of such a collection might or might not be an instance of same for its entire existence. existence dependent collection IntermittentCollection A specialization of both <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> and <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rHIBS0h_TEdaAAABQ2rksLw" class="cyc_term">FirstOrderCollection</a> (qq.v.). This is the collection of all collections of which something can be an instance during (and only during) several non-overlapping periods. For example, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjma5wpEbGdrcN5Y29ycA" class="cyc_term">FamousHuman</a> is an intermittant collection, as a person might be famous as a child, fade into obscurity as a young adult, and then become famous again as an older adult. intermittent collection A collection of collections. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rxyRysnSxEdaAAACgyZzFrg" class="cyc_term">TemporalThingTypeByExistentialStatus</a> is a collection whose members in some way share an existential status, i.e., the extent to which they exist, fail to exist, or their existential history. TemporalThingTypeByExistentialStatus existential attribute NonInitialCollection A specialization of both <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> and <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rHIBS0h_TEdaAAABQ2rksLw" class="cyc_term">FirstOrderCollection</a> (qq.v.). Each instance NIC of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4r_6HdOlV3QdeI9PHEy04DkQ" class="cyc_term">NonInitialCollection</a> is a collection such that nothing can be an instance of NIC at the start of the thing's existence. Thus nothing can be an instance of NIC for its entire existence. Instanceship in NIC is typically "acquired" at some point in time T after the would-be instance INST comes into existence, where T might occur either during or after INST's existence (i.e. "posthumously"). <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4r_6HdOlV3QdeI9PHEy04DkQ" class="cyc_term">NonInitialCollection</a> is agnostic regarding whether INST is an instance of NIC during any period when INST does not exist (cf. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rhs-b2JX9QdeBCoQPSBEw0w" class="cyc_term">ExistenceDependentCollection</a>), and regarding whether INST an instance of NIC "intermittently" (see <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4ra0kFdJX-QdebR5OIAEc_Cg" class="cyc_term">IntermittentCollection</a>). Examples of non-initial collections are <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwQBnMZwpEbGdrcN5Y29ycA" class="cyc_term">AdultAnimal</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVi4PpwpEbGdrcN5Y29ycA" class="cyc_term">Veterinarian</a>, and <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rv4_7sJwpEbGdrcN5Y29ycA" class="cyc_term">MinedArea</a>. non initial collection object type by temporal feature ObjectTypeByTemporalFeature A specialization of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> (q.v.). This is the collection of all and only those collections <code>COL</code> such that any thing's being an instance of <code>COL</code> depends on the current state of the <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjqoZwpEbGdrcN5Y29ycA" class="cyc_term">CycKB</a>. Such a <code>COL</code> corresponds to a property defined (at least partly) in terms of the contents, features, or implementation of the Cyc Knowledge Base itself, as opposed to a property that "exists out there" in the KB-independent world. For example, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvV281JwpEbGdrcN5Y29ycA" class="cyc_term">CycLAssertion</a> is a KB-dependent collection, membership in which requires of a given CycL sentence that it has in fact been asserted to the KB. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViAoJwpEbGdrcN5Y29ycA" class="cyc_term">CycLSentence</a> is also KB-dependent, as being a CycL sentence requires being composed (ultimately) out of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvu6KTZwpEbGdrcN5Y29ycA" class="cyc_term">CycLReifiedDenotationalTerm</a>s (and perhaps variables) -- i.e. terms that are currently reified in the KB. Conversely, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rv5ddsJwpEbGdrcN5Y29ycA" class="cyc_term">Sentence</a> is not a KB-dependent collection. See also <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvip9N5wpEbGdrcN5Y29ycA" class="cyc_term">KBDependentRelation</a>. KB dependent collection KBDependentCollection product type The collection of all types of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVj27ZwpEbGdrcN5Y29ycA" class="cyc_term">PartiallyTangible</a> things that are usually/frequently commercially manufactured. This is context dependent. ManufacturedGoodsType proposition-true A <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rHIBS0h_TEdaAAABQ2rksLw" class="cyc_term">FirstOrderCollection</a>. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rsak66gUwEdqAAAACs2IKaQ" class="cyc_term">Proposition_True</a> in a microtheory or context, MT, is a proposition that is true in that context. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViA7JwpEbGdrcN5Y29ycA" class="cyc_term">Proposition</a>s are the information content of declarative sentences. This collection pick out, in any context, the subcollection of them that are true in that context. We can specify the relation between a true sentence and a true proposition more formally. If S is a sentence that is closed and askable, and P is a proposition such that: (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4raDf58IwOEdmc3QACs1uxFw" class="cyc_term">expresses</a> S P) in <MT, TIME, PAR>, then if S in <MT, TIME, PAR>, then (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViBBJwpEbGdrcN5Y29ycA" class="cyc_term">isa</a> P <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rsak66gUwEdqAAAACs2IKaQ" class="cyc_term">Proposition_True</a>) in <MT, TIME, PAR> Proposition-True GLF graph GLFGraph empty collection A collection of collections and a specialization of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rv1ZxY5wpEbGdrcN5Y29ycA" class="cyc_term">EmptySetOrCollection</a> (q.v.). A collection is an instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rDKZQEKVnQdmACrINeAfsGw" class="cyc_term">EmptyCollection</a> if and only if it has no instances. Some collections are by their very nature necessarily empty; e.g. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rv7LKYpwpEbGdrcN5Y29ycA" class="cyc_term">Nothing</a> (q.v.). Conversely, some collections are empty in some contexts and non-empty in others; e.g. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvhn_I5wpEbGdrcN5Y29ycA" class="cyc_term">Unicorn</a> might be empty in the context of the actual world but non-empty in certain mythological contexts. Similarly, a <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> might be empty at certain times and non-empty at certain other times; e.g. the collection of female US presidents is currently empty but will hopefully become non-empty some time in the near future. This last example demonstrates that <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rDKZQEKVnQdmACrINeAfsGw" class="cyc_term">EmptyCollection</a> is itself a time-dependent collection. Note that each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rDKZQEKVnQdmACrINeAfsGw" class="cyc_term">EmptyCollection</a> is <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViA45wpEbGdrcN5Y29ycA" class="cyc_term">disjointWith</a> (q.v.) every collection -- including itself. Cf. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4r_3mf2qedQdmNjeDW39lDKA" class="cyc_term">NonEmptyCollection</a>. EmptyCollection non empty collection NonEmptyCollection A collection of collections and a specialization of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rVwwqbE7rQdmaWqcELb2oPw" class="cyc_term">NonEmptySetOrCollection</a>. A collection is an instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4r_3mf2qedQdmNjeDW39lDKA" class="cyc_term">NonEmptyCollection</a> if and only if it has at least one instance. Some collections, aguably, are by their very nature necessarily non-empty; e.g. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvl2en5wpEbGdrcN5Y29ycA" class="cyc_term">Set_Mathematical</a>. Conversely, some collections are non-empty in some contexts and empty in others; e.g. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwQBg3ZwpEbGdrcN5Y29ycA" class="cyc_term">Horse</a> is non-empty in the context of the present-day actual world but empty in certain counterfactual contexts in which horses never existed. Similarly, a <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> might be empty at certain times and non-empty at certain other times; e.g. the collection of female US presidents is currently empty but will hopefully become non-empty some time in the near future. This last example demonstrates that <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4r_3mf2qedQdmNjeDW39lDKA" class="cyc_term">NonEmptyCollection</a> is itself a time-dependent collection. Note that each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4r_3mf2qedQdmNjeDW39lDKA" class="cyc_term">NonEmptyCollection</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rlyZyQm22EdaAAACgydogAg" class="cyc_term">intersectsWith</a> (q.v.) <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViA9JwpEbGdrcN5Y29ycA" class="cyc_term">Thing</a>. Cf. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rDKZQEKVnQdmACrINeAfsGw" class="cyc_term">EmptyCollection</a>. A specialization of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViAqJwpEbGdrcN5Y29ycA" class="cyc_term">PropositionalInformationThing</a>. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjb0ZwpEbGdrcN5Y29ycA" class="cyc_term">News</a> consists of some factual information about recent events in the world (or <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjNiZwpEbGdrcN5Y29ycA" class="cyc_term">geographicalSubRegions</a> thereof). News is commonly embodied in newspapers and communicated through radio and television news broadcasts. Note that <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjb0ZwpEbGdrcN5Y29ycA" class="cyc_term">News</a> does not include as instances any instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwEdlDZwpEbGdrcN5Y29ycA" class="cyc_term">NewsArticle</a> (q.v.). Rather, an instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjb0ZwpEbGdrcN5Y29ycA" class="cyc_term">News</a> might be the content of a <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwEdlDZwpEbGdrcN5Y29ycA" class="cyc_term">NewsArticle</a>, and could be the content of distinct <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwEdlDZwpEbGdrcN5Y29ycA" class="cyc_term">NewsArticle</a>s news News A collection of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjl_ZwpEbGdrcN5Y29ycA" class="cyc_term">SetOrCollection</a>s. A set or collection is an instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rVwwqbE7rQdmaWqcELb2oPw" class="cyc_term">NonEmptySetOrCollection</a> if and only if it has at least one element. Cf. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rv1ZxY5wpEbGdrcN5Y29ycA" class="cyc_term">EmptySetOrCollection</a>. non empty set or collection NonEmptySetOrCollection ThingConformingToKosherDietaryLaws This is the attribute of being kosher. Being kosher means conforming to Jewish laws dealing with food. The attribute can apply to anthing related to food: kitchens, slaughtering techniques, diets, food items. kosher thing A specialization of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> (q.v.). This is the collection of all and only those collections <code>COL</code> such that any thing's being an instance of <code>COL</code> depends on the current state of the <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjqoZwpEbGdrcN5Y29ycA" class="cyc_term">CycKB</a>. Such a <code>COL</code> corresponds to a property defined (at least partly) in terms of the contents, features, or implementation of the Cyc Knowledge Base itself, as opposed to a property that "exists out there" in the KB-independent world. For example, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvV281JwpEbGdrcN5Y29ycA" class="cyc_term">CycLAssertion</a> is a KB-dependent collection, membership in which requires of a given CycL sentence that it has in fact been asserted to the KB. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViAoJwpEbGdrcN5Y29ycA" class="cyc_term">CycLSentence</a> is also KB-dependent, as being a CycL sentence requires being composed (ultimately) out of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvu6KTZwpEbGdrcN5Y29ycA" class="cyc_term">CycLReifiedDenotationalTerm</a>s (and perhaps variables) -- i.e. terms that are currently reified in the KB. Conversely, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rv5ddsJwpEbGdrcN5Y29ycA" class="cyc_term">Sentence</a> is not a KB-dependent collection. See also <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvip9N5wpEbGdrcN5Y29ycA" class="cyc_term">KBDependentRelation</a>. KB dependent collection KBDependentCollection Business-Fortune500 A specialization of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViSTpwpEbGdrcN5Y29ycA" class="cyc_term">LargeIncorporatedBusiness</a>. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rfGs25jXuEdqAAAACs6hRXg" class="cyc_term">Business_Fortune500</a> is among the largest 500 corporations in the U.S. during a particular year, according to the editors of Fortune Magazine. Fortune 500 company A collection of collections. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> is a collection whose membership changes over time. For example, (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX35wpEbGdrcN5Y29ycA" class="cyc_term">LiquidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) is a time dependent collection. A given portion of water might be an instance of (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX35wpEbGdrcN5Y29ycA" class="cyc_term">LiquidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) in the summer, and an instance of the disjoint collection (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX0JwpEbGdrcN5Y29ycA" class="cyc_term">SolidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) in the winter. In contrast, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVieEpwpEbGdrcN5Y29ycA" class="cyc_term">Integer</a> is a <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvzndCZwpEbGdrcN5Y29ycA" class="cyc_term">TimeIndependentCollection</a> (q.v.) because the collection of integers does not change its membership over time. time dependent collection TimeDependentCollection candidate KB completeness node CandidateKBCompletenessNode TimeIndependentCollection time independent collection A collection of collections. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvzndCZwpEbGdrcN5Y29ycA" class="cyc_term">TimeIndependentCollection</a> is a collection whose membership cannot change over time. Examples of time-independent collections are <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvxwC-ZwpEbGdrcN5Y29ycA" class="cyc_term">Number_General</a> and <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rv0YfN5wpEbGdrcN5Y29ycA" class="cyc_term">MathematicalObject</a>. By contrast, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwFronJwpEbGdrcN5Y29ycA" class="cyc_term">Supermodel</a> is clearly a <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> (q.v.). A collection of collections. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a> is a collection whose membership changes over time. For example, (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX35wpEbGdrcN5Y29ycA" class="cyc_term">LiquidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) is a time dependent collection. A given portion of water might be an instance of (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX35wpEbGdrcN5Y29ycA" class="cyc_term">LiquidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) in the summer, and an instance of the disjoint collection (<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzX0JwpEbGdrcN5Y29ycA" class="cyc_term">SolidFn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjAHZwpEbGdrcN5Y29ycA" class="cyc_term">Water</a>) in the winter. In contrast, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVieEpwpEbGdrcN5Y29ycA" class="cyc_term">Integer</a> is a <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvzndCZwpEbGdrcN5Y29ycA" class="cyc_term">TimeIndependentCollection</a> (q.v.) because the collection of integers does not change its membership over time. time dependent collection TimeDependentCollection type of thing Collection A specialization of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjl_ZwpEbGdrcN5Y29ycA" class="cyc_term">SetOrCollection</a> (q.v.). This is the collection of all collections of things. Each <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViAzJwpEbGdrcN5Y29ycA" class="cyc_term">Collection</a> is a kind or type of thing whose instances share a certain property, attribute, or feature. For example, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVkFc5wpEbGdrcN5Y29ycA" class="cyc_term">Cat</a> is the collection of all and only cats, and <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwOckfJwpEbGdrcN5Y29ycA" class="cyc_term">BinaryFunction</a> 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 <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvl2en5wpEbGdrcN5Y29ycA" class="cyc_term">Set_Mathematical</a>). Like a set, a collection is an <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rpJ-nSEkJQdeC8NLkYPDBBw" class="cyc_term">AbstractThing</a> (i.e. aspatial and atemporal) that is not an <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVjaApwpEbGdrcN5Y29ycA" class="cyc_term">Individual</a> (cf.), but instead has elements (see <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwGWaK5wpEbGdrcN5Y29ycA" class="cyc_term">elementOf</a>). Unlike a set, however, the elements or "instances" (see <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViBBJwpEbGdrcN5Y29ycA" class="cyc_term">isa</a>) 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 <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwN2YGZwpEbGdrcN5Y29ycA" class="cyc_term">extent</a>) 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. '(<a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwEcGC5wpEbGdrcN5Y29ycA" class="cyc_term">CollectionIntersection2Fn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVkFc5wpEbGdrcN5Y29ycA" class="cyc_term">Cat</a> <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rBjWwGHS-EdaAAACgyZzFrg" class="cyc_term">WhiteColor</a>)'), and because there's not much to say about that particular collection. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rsX6vHnS6EdaAAACgyZzFrg" class="cyc_term">WhiteCollarWorker</a>, 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 <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViAzJwpEbGdrcN5Y29ycA" class="cyc_term">Collection</a> are <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rHIBS0h_TEdaAAABQ2rksLw" class="cyc_term">FirstOrderCollection</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwIE23ZwpEbGdrcN5Y29ycA" class="cyc_term">TimeDependentCollection</a>, and <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvVirnZwpEbGdrcN5Y29ycA" class="cyc_term">ObjectType</a>. A collection of collections of collections. <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvtppU5wpEbGdrcN5Y29ycA" class="cyc_term">CollectionType</a> is the collection of all (and only) types of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViAzJwpEbGdrcN5Y29ycA" class="cyc_term">Collection</a>s. More precisely, a thing COLLTYPE is an instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvtppU5wpEbGdrcN5Y29ycA" class="cyc_term">CollectionType</a> if and only if COLLTYPE is a non-empty collection all of whose instances are collections. Example: <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rwPzQbJwpEbGdrcN5Y29ycA" class="cyc_term">PersonTypeByCulture</a>, each of whose instances is the collection of all persons who participate in some particular human culture, is an instance of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvtppU5wpEbGdrcN5Y29ycA" class="cyc_term">CollectionType</a>. Important specializations of <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvtppU5wpEbGdrcN5Y29ycA" class="cyc_term">CollectionType</a> include <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvWPoRpwpEbGdrcN5Y29ycA" class="cyc_term">DisjointCollectionType</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rvViA4pwpEbGdrcN5Y29ycA" class="cyc_term">SiblingDisjointCollectionType</a>, and <a href="http://sw.opencyc.org/2008/06/10/concept/Mx4rviPYH5wpEbGdrcN5Y29ycA" class="cyc_term">CollectionTypeType</a>. CollectionType type of collection