]> 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. isa is a Mx4rvViBBJwpEbGdrcN5Y29ycA A <a href="http://sw.opencyc.org/2008/06/10/concept/en/TaxonomicSlot" class="cyc_term">TaxonomicSlot</a> (q.v.) that relates things of any kind to collections (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/Collection" class="cyc_term">Collection</a>) of which they are instances. <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING COL)</code> means that <code>THING</code> is an instance of the collection <code>COL</code>. <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> is by far the most commonly-occurring predicate in the Cyc Knowledge Base, and is one of the relations most fundamental to the Cyc ontology. An important logical feature of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> is that it "transfers through" <a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a> (q.v.): <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING COL)</code> and <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a> COL SUPERCOL)</code> jointly imply <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING SUPERCOL)</code>. This logical feature is expressed in a rule that -- along with various other rules that also sanction the derivation of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> sentences -- has been asserted to the Knowledge Base. As a result, only a small fraction of the <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> based ground atomic formulas (or "GAF"s; see <a href="http://sw.opencyc.org/2008/06/10/concept/en/CycLClosedAtomicSentence" class="cyc_term">CycLClosedAtomicSentence</a>) the Cyc system "knows" to be true have been manually asserted; the vast majority have been derived, or are derivable, automatically by the Cyc inference engine via the use of such rules. See also <a href="http://sw.opencyc.org/2008/06/10/concept/en/elementOf" class="cyc_term">elementOf</a>. The collection of Cyc FORTs that are not relevant to the reformulator. ReformulatorIrrelevantFORT reformulator irrelevant FORT WFF constraint satisfaction predicate WFFConstraintSatisfactionPredicate The collection of all <a href="http://sw.opencyc.org/2008/06/10/concept/en/Predicate" class="cyc_term">Predicate</a>s which can satisfy well-formedness constraints. More specifically, only assertions of the form (PRED . ARGS), where PRED is an instance of <a href="http://sw.opencyc.org/2008/06/10/concept/en/WFFConstraintPredicate" class="cyc_term">WFFConstraintPredicate</a>, can directly satisfy a well-formedness constraint, i.e. cause any previously ill-formed sentence to become well-formed, given the same WFF standards. Any assertion could _indirectly_ satisfy a well-formedness constraint, for instance by triggering a forward rule or an <a href="http://sw.opencyc.org/2008/06/10/concept/en/afterAdding" class="cyc_term">afterAdding</a>. A common case of this is the <a href="http://sw.opencyc.org/2008/06/10/concept/en/afterAdding" class="cyc_term">afterAdding</a>s on spec-preds of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> and <a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a>. isa is a A <a href="http://sw.opencyc.org/2008/06/10/concept/en/TaxonomicSlot" class="cyc_term">TaxonomicSlot</a> (q.v.) that relates things of any kind to collections (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/Collection" class="cyc_term">Collection</a>) of which they are instances. <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING COL)</code> means that <code>THING</code> is an instance of the collection <code>COL</code>. <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> is by far the most commonly-occurring predicate in the Cyc Knowledge Base, and is one of the relations most fundamental to the Cyc ontology. An important logical feature of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> is that it "transfers through" <a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a> (q.v.): <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING COL)</code> and <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a> COL SUPERCOL)</code> jointly imply <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING SUPERCOL)</code>. This logical feature is expressed in a rule that -- along with various other rules that also sanction the derivation of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> sentences -- has been asserted to the Knowledge Base. As a result, only a small fraction of the <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> based ground atomic formulas (or "GAF"s; see <a href="http://sw.opencyc.org/2008/06/10/concept/en/CycLClosedAtomicSentence" class="cyc_term">CycLClosedAtomicSentence</a>) the Cyc system "knows" to be true have been manually asserted; the vast majority have been derived, or are derivable, automatically by the Cyc inference engine via the use of such rules. See also <a href="http://sw.opencyc.org/2008/06/10/concept/en/elementOf" class="cyc_term">elementOf</a>. thing <a href="http://sw.opencyc.org/2008/06/10/concept/en/Thing" class="cyc_term">Thing</a> is the "universal collection": the collection which, by definition, contains everything there is. Every thing in the Cyc ontology -- every <a href="http://sw.opencyc.org/2008/06/10/concept/en/Individual" class="cyc_term">Individual</a> (of any kind), every <a href="http://sw.opencyc.org/2008/06/10/concept/en/Set_Mathematical" class="cyc_term">Set_Mathematical</a>, and every <a href="http://sw.opencyc.org/2008/06/10/concept/en/Collection" class="cyc_term">Collection</a> -- is an instance of (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a>) <a href="http://sw.opencyc.org/2008/06/10/concept/en/Thing" class="cyc_term">Thing</a>. Similarly, every collection is a subcollection of (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a>) <a href="http://sw.opencyc.org/2008/06/10/concept/en/Thing" class="cyc_term">Thing</a>. Trivially, <a href="http://sw.opencyc.org/2008/06/10/concept/en/Thing" class="cyc_term">Thing</a> is both an instance of and a subcollection of itself, and is not a subcollection of any other collection. (Note that the above reference to "every thing in the Cyc ontology" is not meant to be limited to things actually reified in the Cyc system, but includes (e.g.) every instance -- reified or not, known or not -- of every collection recognized by Cyc.) Thing isa is a A <a href="http://sw.opencyc.org/2008/06/10/concept/en/TaxonomicSlot" class="cyc_term">TaxonomicSlot</a> (q.v.) that relates things of any kind to collections (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/Collection" class="cyc_term">Collection</a>) of which they are instances. <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING COL)</code> means that <code>THING</code> is an instance of the collection <code>COL</code>. <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> is by far the most commonly-occurring predicate in the Cyc Knowledge Base, and is one of the relations most fundamental to the Cyc ontology. An important logical feature of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> is that it "transfers through" <a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a> (q.v.): <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING COL)</code> and <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a> COL SUPERCOL)</code> jointly imply <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING SUPERCOL)</code>. This logical feature is expressed in a rule that -- along with various other rules that also sanction the derivation of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> sentences -- has been asserted to the Knowledge Base. As a result, only a small fraction of the <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> based ground atomic formulas (or "GAF"s; see <a href="http://sw.opencyc.org/2008/06/10/concept/en/CycLClosedAtomicSentence" class="cyc_term">CycLClosedAtomicSentence</a>) the Cyc system "knows" to be true have been manually asserted; the vast majority have been derived, or are derivable, automatically by the Cyc inference engine via the use of such rules. See also <a href="http://sw.opencyc.org/2008/06/10/concept/en/elementOf" class="cyc_term">elementOf</a>. A subcollection of <a href="http://sw.opencyc.org/2008/06/10/concept/en/TaxonomicSlot" class="cyc_term">TaxonomicSlot</a> (q.v.). Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/en/TaxonomicSlotForAnyThing" class="cyc_term">TaxonomicSlotForAnyThing</a> is a taxonomic slot that can in principle be used to help specify the location of anything whatsoever within some taxonomy; hence at least one of its argument-places must be constrained to instances (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/argIsa" class="cyc_term">argIsa</a>) of <a href="http://sw.opencyc.org/2008/06/10/concept/en/Thing" class="cyc_term">Thing</a> (and to nothing more specific than <a href="http://sw.opencyc.org/2008/06/10/concept/en/Thing" class="cyc_term">Thing</a>). Examples include <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> and <a href="http://sw.opencyc.org/2008/06/10/concept/en/generalizations" class="cyc_term">generalizations</a>. TaxonomicSlotForAnyThing Cyc taxonomic predicate applicable to anything SetOrCollectionPredicate intensional representation predicate The <a href="http://sw.opencyc.org/2008/06/10/concept/en/PredicateType" class="cyc_term">PredicateType</a> consisting of all predicates that (always) hold of <a href="http://sw.opencyc.org/2008/06/10/concept/en/SetOrCollection" class="cyc_term">SetOrCollection</a>s (q.v.). Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/en/SetOrCollectionPredicate" class="cyc_term">SetOrCollectionPredicate</a> has at least one argument-place constrained to instances (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/argIsa" class="cyc_term">argIsa</a>) of <a href="http://sw.opencyc.org/2008/06/10/concept/en/SetOrCollection" class="cyc_term">SetOrCollection</a> or some specialization thereof. Some set-or-collection predicates are used to make statements that are more or less directly about a given set-or-collection itself (e.g. <a href="http://sw.opencyc.org/2008/06/10/concept/en/cardinality" class="cyc_term">cardinality</a> relates a set-or-collection to its size); but most are used to make more general statements about some or all of the elements of a given set-or-collection (e.g. <a href="http://sw.opencyc.org/2008/06/10/concept/en/inhabitantTypes" class="cyc_term">inhabitantTypes</a> relates a geographical region to a collection of persons such that at least one person in the collection resides in that region). Specializations of <a href="http://sw.opencyc.org/2008/06/10/concept/en/SetOrCollectionPredicate" class="cyc_term">SetOrCollectionPredicate</a> include <a href="http://sw.opencyc.org/2008/06/10/concept/en/FirstOrderCollectionPredicate" class="cyc_term">FirstOrderCollectionPredicate</a> and <a href="http://sw.opencyc.org/2008/06/10/concept/en/RuleMacroPredicate" class="cyc_term">RuleMacroPredicate</a>. Cf. <a href="http://sw.opencyc.org/2008/06/10/concept/en/ObjectPredicate" class="cyc_term">ObjectPredicate</a>. A <a href="http://sw.opencyc.org/2008/06/10/concept/en/CycVocabularyTopic" class="cyc_term">CycVocabularyTopic</a> and a <a href="http://sw.opencyc.org/2008/06/10/concept/en/KBDependentCollection" class="cyc_term">KBDependentCollection</a>. Basics-Fundamental-Topic basics-fundamental-topic DefaultMonotonicPredicate A collection of predicates. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/en/DefaultMonotonicPredicate" class="cyc_term">DefaultMonotonicPredicate</a> is a predicate whose use as the predicate of a locally asserted ground formula causes that formula to be entered, by default, as :MONOTONIC. Examples: <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/en/disjointWith" class="cyc_term">disjointWith</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/en/equals" class="cyc_term">equals</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/en/arity" class="cyc_term">arity</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/en/arg1Isa" class="cyc_term">arg1Isa</a>. default monotonic predicate SOEDefaultGraphablePredicate SOE default graphable predicate FactGatheringForbiddenPredicate A sub-collection of <a href="http://sw.opencyc.org/2008/06/10/concept/en/Predicate" class="cyc_term">Predicate</a>. Each instance of <a href="http://sw.opencyc.org/2008/06/10/concept/en/FactGatheringForbiddenPredicate" class="cyc_term">FactGatheringForbiddenPredicate</a> is a predicate which should not be used for fact gathering. fact gathering forbidden predicate The collection of all <a href="http://sw.opencyc.org/2008/06/10/concept/en/Relation" class="cyc_term">Relation</a>s whose extentions (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/relationExtension" class="cyc_term">relationExtension</a>) change, at least somewhat, over time. A relation <code>RELN</code> is an instance of <a href="http://sw.opencyc.org/2008/06/10/concept/en/TemporallyQualifiableRelation" class="cyc_term">TemporallyQualifiableRelation</a> if and only if there is sequence <code>SEQ</code> and times <code>T1</code> and <code>T2</code> such that <code>RELN</code> holds among <code>SEQ</code> at <code>T1</code> but not at <code>T2</code>. Note that <code>RELN</code> might nevertheless hold of some sequences eternally. An example of such a relation is <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a>. On the one hand, the sentence <pre> (<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> <a href="http://sw.opencyc.org/2008/06/10/concept/en/GeorgeWBush" class="cyc_term">GeorgeWBush</a> <a href="http://sw.opencyc.org/2008/06/10/concept/en/UnitedStatesPresident" class="cyc_term">UnitedStatesPresident</a>) </pre> is true at some times and false at others, and so requires temporal qualification. On the other hand, the sentence <pre> (<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> <a href="http://sw.opencyc.org/2008/06/10/concept/en/UnitedStatesPresident" class="cyc_term">UnitedStatesPresident</a> <a href="http://sw.opencyc.org/2008/06/10/concept/en/FirstOrderCollection" class="cyc_term">FirstOrderCollection</a>) </pre> is true eternally and requires no temporal qualification. If a given temporally-qualifiable relation holds of no sequences eternally (e.g. <a href="http://sw.opencyc.org/2008/06/10/concept/en/likesAsFriend" class="cyc_term">likesAsFriend</a>), it is an instance of the specialization <a href="http://sw.opencyc.org/2008/06/10/concept/en/TimeDependentCollection" class="cyc_term">TimeDependentCollection</a> (q.v.). Cf. <a href="http://sw.opencyc.org/2008/06/10/concept/en/TimeIndependentRelation" class="cyc_term">TimeIndependentRelation</a>. temporally qualifiable relation TemporallyQualifiableRelation isa is a A <a href="http://sw.opencyc.org/2008/06/10/concept/en/TaxonomicSlot" class="cyc_term">TaxonomicSlot</a> (q.v.) that relates things of any kind to collections (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/Collection" class="cyc_term">Collection</a>) of which they are instances. <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING COL)</code> means that <code>THING</code> is an instance of the collection <code>COL</code>. <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> is by far the most commonly-occurring predicate in the Cyc Knowledge Base, and is one of the relations most fundamental to the Cyc ontology. An important logical feature of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> is that it "transfers through" <a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a> (q.v.): <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING COL)</code> and <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/genls" class="cyc_term">genls</a> COL SUPERCOL)</code> jointly imply <code>(<a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> THING SUPERCOL)</code>. This logical feature is expressed in a rule that -- along with various other rules that also sanction the derivation of <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> sentences -- has been asserted to the Knowledge Base. As a result, only a small fraction of the <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" class="cyc_term">isa</a> based ground atomic formulas (or "GAF"s; see <a href="http://sw.opencyc.org/2008/06/10/concept/en/CycLClosedAtomicSentence" class="cyc_term">CycLClosedAtomicSentence</a>) the Cyc system "knows" to be true have been manually asserted; the vast majority have been derived, or are derivable, automatically by the Cyc inference engine via the use of such rules. See also <a href="http://sw.opencyc.org/2008/06/10/concept/en/elementOf" class="cyc_term">elementOf</a>. Analyst-PertinentConcept An instance of <a href="http://sw.opencyc.org/2008/06/10/concept/en/ConceptTypeByDomain" class="cyc_term">ConceptTypeByDomain</a>. Generally speaking, instances of <a href="http://sw.opencyc.org/2008/06/10/concept/en/Analyst_PertinentConcept" class="cyc_term">Analyst_PertinentConcept</a> are concepts and relations such as are used by intelligence analysts reasoning about threat situations. Specifically, all core concepts in this domain (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/coreConceptOfDomain" class="cyc_term">coreConceptOfDomain</a>) are either 1) <a href="http://sw.opencyc.org/2008/06/10/concept/en/BinaryPredicate" class="cyc_term">BinaryPredicate</a>s referenced in AKB Fact Entry Templates, 2) <a href="http://sw.opencyc.org/2008/06/10/concept/en/TernaryPredicate" class="cyc_term">TernaryPredicate</a>s referenced in AKB Fact Entry Templates, 3:)<a href="http://sw.opencyc.org/2008/06/10/concept/en/FirstOrderCollection" class="cyc_term">FirstOrderCollection</a>s that are asserted to be <a href="http://sw.opencyc.org/2008/06/10/concept/en/argIsa" class="cyc_term">argIsa</a>s of <a href="http://sw.opencyc.org/2008/06/10/concept/en/BinaryPredicate" class="cyc_term">BinaryPredicate</a>s referenced in AKB Fact Entry Templates, 4) <a href="http://sw.opencyc.org/2008/06/10/concept/en/FirstOrderCollection" class="cyc_term">FirstOrderCollection</a>s that are asserted to be <a href="http://sw.opencyc.org/2008/06/10/concept/en/argIsa" class="cyc_term">argIsa</a>s of <a href="http://sw.opencyc.org/2008/06/10/concept/en/TernaryPredicate" class="cyc_term">TernaryPredicate</a>s referenced in AKB Fact Entry Templates, 5) <a href="http://sw.opencyc.org/2008/06/10/concept/en/FirstOrderCollection" class="cyc_term">FirstOrderCollection</a>s that are asserted to be <a href="http://sw.opencyc.org/2008/06/10/concept/en/argGenl" class="cyc_term">argGenl</a>s of <a href="http://sw.opencyc.org/2008/06/10/concept/en/TernaryPredicate" class="cyc_term">TernaryPredicate</a>s referenced in AKB Fact Entry Templates, or 6) concepts or relations that are instances of instances of #$TKBInterfaceCollection. the intelligence analyst reasoning domain type of thing A specialization of <a href="http://sw.opencyc.org/2008/06/10/concept/en/SetOrCollection" 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/en/Collection" 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/en/Cat" class="cyc_term">Cat</a> is the collection of all and only cats, and <a href="http://sw.opencyc.org/2008/06/10/concept/en/BinaryFunction" 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/en/Set_Mathematical" class="cyc_term">Set_Mathematical</a>). Like a set, a collection is an <a href="http://sw.opencyc.org/2008/06/10/concept/en/AbstractThing" class="cyc_term">AbstractThing</a> (i.e. aspatial and atemporal) that is not an <a href="http://sw.opencyc.org/2008/06/10/concept/en/Individual" class="cyc_term">Individual</a> (cf.), but instead has elements (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/elementOf" class="cyc_term">elementOf</a>). Unlike a set, however, the elements or "instances" (see <a href="http://sw.opencyc.org/2008/06/10/concept/en/isa" 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/en/extent" 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/en/CollectionIntersection2Fn" class="cyc_term">CollectionIntersection2Fn</a> <a href="http://sw.opencyc.org/2008/06/10/concept/en/Cat" class="cyc_term">Cat</a> <a href="http://sw.opencyc.org/2008/06/10/concept/en/WhiteColor" 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/en/WhiteCollarWorker" 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/en/Collection" class="cyc_term">Collection</a> are <a href="http://sw.opencyc.org/2008/06/10/concept/en/FirstOrderCollection" class="cyc_term">FirstOrderCollection</a>, <a href="http://sw.opencyc.org/2008/06/10/concept/en/TimeDependentCollection" class="cyc_term">TimeDependentCollection</a>, and <a href="http://sw.opencyc.org/2008/06/10/concept/en/ObjectType" class="cyc_term">ObjectType</a>. Collection <a href="http://sw.opencyc.org/2008/06/10/concept/en/HLPredicate" class="cyc_term">HLPredicate</a> is the collection of all Cyc predicates which have special HL support. HL predicate HLPredicate vocabulary defining predicate VocabularyDefiningPredicate The collection of all <a href="http://sw.opencyc.org/2008/06/10/concept/en/Predicate" class="cyc_term">Predicate</a>s that are considered sufficiently ``definitional'' for a term for assertions using such <a href="http://sw.opencyc.org/2008/06/10/concept/en/VocabularyDefiningPredicate" class="cyc_term">VocabularyDefiningPredicate</a>s to be stated in a <a href="http://sw.opencyc.org/2008/06/10/concept/en/definingMt" class="cyc_term">definingMt</a> <a href="http://sw.opencyc.org/2008/06/10/concept/en/VocabularyMicrotheory" class="cyc_term">VocabularyMicrotheory</a>. SagemanProfileTerm sageman profile term