Help:Basic membership properties

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Afrikaans • ‎العربية • ‎bosanski • ‎català • ‎čeština • ‎Cymraeg • ‎dansk • ‎Deutsch • ‎English • ‎British English • ‎Esperanto • ‎español • ‎euskara • ‎فارسی • ‎français • ‎Frysk • ‎हिन्दी • ‎Հայերեն • ‎italiano • ‎日本語 • ‎한국어 • ‎Ripoarisch • ‎Lëtzebuergesch • ‎lietuvių • ‎latviešu • ‎македонски • ‎Bahasa Melayu • ‎norsk bokmål • ‎Nederlands • ‎occitan • ‎polski • ‎پښتو • ‎português • ‎português do Brasil • ‎русский • ‎Scots • ‎shqip • ‎தமிழ் • ‎తెలుగు • ‎тоҷикӣ • ‎ไทย • ‎Türkçe • ‎українська • ‎中文

Introduction[edit]

This page explains the differences between the properties instance of (P31), subclass of (P279) and part of (P361). To understand the differences, it is important to be familiar with the terms instance and class.

Definitions[edit]

instance:

  • an individual or a single thing

class:

  • an abstract object that abstracts instances;
  • each class is characterized by some feature that all of its instances share;
  • can share instances with other class but be distinct from other class[1]

Examples:

Practical aspects[edit]

  • Item can either be an instance and/or a class;
  • Multiple instances can be abstracted into class A;
  • Same is possible without instances at Wikidata: class is kept in Wikidata, when instances are created in other places;
  • Some class A can be abstracted into class B, relation between A and B is called subclass of.

instance of (P31)[edit]

The relation between instances with a common feature and a class characterized by this feature is produced with the property instance of (P31). We use instance of (P31) instead of subclass of (P279) when we cannot say anything about instances with such relation. More specifically, it is a rdf:type.[2]

For example, Atlantic Ocean (Q97) and Pacific Ocean (Q98) are both instances of ocean (Q9430). We write therefore on Wikidata:

subclass of (P279)[edit]

  • is used to state that all the instances of one class are instances of another[3]
  • more specifically, it is a rdfs:subClassOf[4]

Several examples:

Another example:

A lake and an ocean is not the same but all their instances share the common feature of being a body of water. Therefore we can use the class body of water (Q15324) to state that:

Now Lake Baikal (Q5513), Lake Erie (Q5492), Atlantic Ocean (Q97) and Pacific Ocean (Q98) will all be transitive (indirect) instances of body of water (Q15324). In general we can use more abstract objects (like body of water (Q15324)) instead of enumerations (lake (Q23397) and ocean (Q9430)) both: 1. in our statements and 2. in our questions (not covered at this help page).

subclass of (P279) is transitive property (Q18647515), that means if an item A is an instance of class B, and class B is a subclass of class C, item A is implicitly also an instance of class C. There is no general need to add a statement for the relation A→C to Wikidata.

For example, Lighthouse of Alexandria (Q43244) is an instance of lighthouse (Q39715) and lighthouse (Q39715) is a subclass of tower (Q12518). Lighthouse of Alexandria (Q43244) is thus an instance of tower (Q12518).

part of (P361)[edit]

Items can not be instance of another instance but they can be part of another instance. For example, Albert Einstein's brain (Q2464312) is a part of Albert Einstein (Q937). On Wikidata we use part of (P361) for this relation.

Classes can also be part of another class. For example,

The use of instance of (P31) instead of part of (P361) would be wrong here because human brain (Q492038) is not a single thing and thus not an instance. Using subclass of (P279) would also be wrong because an instance of human brain (Q492038) (e.g. Albert Einstein's brain (Q2464312)) is not an instance of the class Homo sapiens (Q15978631).

The third way to use part of (P361) is in a class-instance relation. If all instances of a class A are part of instance B, one can state that class A is part of instance B.

For example,

Like subclass of (P279), part of (P361) is a transitive property.

Inverse relations of part of (P361)[edit]

  1. has part (P527) - is used to say that an instance is composed of other instances
  2. has parts of the class (P2670) - denotes that an instance or a class is made out of other classes

For example,

In the first example, has part (P527) is used because Α (Q9887) is an instance. In the latter two examples, we take has parts of the class (P2670) since Greek letter (Q19793459) and letter (Q9788) are classes.

Examples[edit]

Differences among instance of (P31), subclass of (P279) and part of (P361)
property X Y what it denotes example explanation why not use ...
<X> instance of <Y> instance class
  • X is an individual (single thing) belonging to class Y
  • X is a specific example of class Y
  • all instances of class Y share certain features
  • Y is the set of its instances (including X)
<USS Nimitz> instance of <supercarrier> <USS Nimitz> is a single concrete aircraft carrier, <supercarrier> is an aircraft carrier class which has many instances (aircraft carriers)
  • subclass of not used because <USS Nimitz> is not a class
  • part of not used because <USS Nimitz> is an instance and the <supercarrier> is a class, instances cannot be parts of classes
<People's Republic of China> instance of <sovereign state> <sovereign state> is a concept defined by some features, <China> is an object which meet these features
  • subclass of not used because <China> is a concrete state
  • part of not used because instances cannot be parts of classes
<Sun> instance of <G-type main-sequence star> The <Sun> is a specific star with the spectral characteristics of a G-type main-sequence star, and so is an instance of that class * subclass of not used because the <Sun> is not a class but a single astronomical object
  • part of not used because non-classes cannot be parts of classes
<hatter> instance of <profession> <hatter> is a specific example of a profession
  • subclass of not used because <hatter> is not a class of professions but a single profession (instance)
  • part of not used because instances cannot be parts of classes
<Douglas Adams> instance of <human> <Douglas Adams> is a specific human person (this is one of the most common cases for instance of) * subclass of not used because <Douglas Adams> is not a class of people but a single person (instance)
  • part of not used because instances cannot be parts of classes
<X> subclass of <Y> class class
  • all instances of class X belong to class Y
  • instances of X are also instances of Y
<supercarrier> subclass of <aircraft carrier> both <supercarrier> and <aircraft carrier> are classes and the latter contains the former
  • instance of not used because <supercarrier> is not a concrete object
  • part of not used because an instance of <supercarrier> (e.g. <USS Nimitz>) cannot be part of an instance of aircraft carrier (e.g. <{{label|USS Enterprise>)
<sovereign state> subclass of <state> both of them are classes, the former has all features of the latter and some additional features, so it is a subclass of the latter
  • instance of not used because <sovereign state> is not a specific state, but a class that contains all sovereign states
  • part of not used because an instance of the sovereign state (e.g. <China>) cannot be part of an instance of state (e.g. <China>)
<G-type star> subclass of <star> every individual G-class star (instances of <G-class star>) is also a star - i.e. belongs to the class <star> * instance of not used because <G-class star> is not a single star, but a type of <star>
  • part of not used because the relationship is not one of composition, i.e. individual <G-class star> instances do not join together to make an instance of a <star>.
<X> part of <Y> instance instance
  • instance X is a part of instance Y
  • different parts of Y (including X) combine together to form the whole Y
<USS Nimitz> part of <Carrier Strike Group Eleven> <USS Nimitz> is a concrete aircraft carrier, <CSG-11> is a concrete carrier strike group, <USS Nimitz> is one of <CSG-11>'s components (its flagship)
  • instance of not used because <CSG-11> is not a class
  • subclass of not used because neither of them is a class
<People's Republic of China> part of <Asia> both <China> and <Asia> are specific geographic features, <China> is part of the continent <Asia>
  • instance of not used because <Asia> is an instance (meanwhile <Asian country> is a class so you could say <China> is an instance of <Asian country>)
  • subclass of not used because neither of them is a class
<Sun> part of <Solar System> both of them are individual astronomical objects; the solar system is composed of the Sun, planets, and other objects in the Sun's vicinity * instance of not used because the latter is an individual astronomical object, not a generic concept
  • subclass of not used because neither of them is a class
class class

an instance of class X is part of an instance of class Y

<flight deck> part of <aircraft carrier> every aircraft carrier (instance of <aircraft carrier>) has its own flight deck (instance of <flight deck>)
  • instance of not used because <flight deck> is a class not an instance (only a specific flight deck, such as the <flight deck of USS Nimitz>, can be an instance)
  • subclass of not used because an instance of the former (e.g. <flight deck of USS Nimitz>) cannot be the same thing as an instance of the latter (e.g. <USS Nimitz>)
<member state> part of <international organization> an instance of <member state> is a component of an instance of <international organization>
  • instance of not used because the former is a concept, does not indicate any specific state (e.g. <China>)
  • subclass of not used because an instance of <member state> does not belong to the class <international organization> (e.g. China is not an international organization)
<star> part of <galaxy> a star typically is born and lives within a single galaxy which is made up of many stars and other astronomical objects
  • instance of not used because <star> is not an example of a <galaxy>
  • subclass of not used because instances of class <star> are not instances of the class <galaxy>
class instance every instance of X is a part of item Y <inner planet of the Solar System> part of <Solar System> every inner planet belongs to our Solar System
  • instance of not used because the <Solar System> is not a class and the <inner planets> are not an example of it
  • subclass of not used because <Solar System> is not a class, and particular <inner planets> are not examples of it
<college of the University of Cambridge> part of <University of Cambridge> every particular college of the University of Cambridge is a part of that University
  • instance of not used because the <University of Cambridge> is not a class and the class of its colleges are not an example of it
  • subclass of not used because <University of Cambridge> is not a class, and particular colleges are not examples of it
  • Note: some examples above are for demonstration purposes only, which should not be used in Wikidata because there are more specific relationships that should be used (e.g. use "<China> continent <Asia>" instead of "<China> part of <Asia>").
Differences among has part (P527) and has parts of the class (P2670)
property X Y what it denotes example explanation why not use ...
<X> has part <Y> instance instance instance X has instance Y among its parts or components <United States Congress> has part <United States Senate> the US Congress has two parts, the House of Representatives and the Senate
  • has parts of the class not used because <United States Senate> is not a class
<Solar System> has part <Mars> <Mars> is one of the planets in the <Solar System>
  • has parts of the class not used because <Mars> is not a class
<X> has parts of the class <Y> class class an instance of X has an instance of Y among its parts or components <body> has parts of the class <head> in general a <body> (anatomical feature) has a <head> as one of its parts
  • has part not used because <head> is not an instance
<galaxy> has parts of the class <star> a <galaxy> has <stars> as one of its parts
  • has part not used because <star> is not an instance
instance class the specific item X includes every instance of class Y among its parts or components <University of Cambridge> has parts of the class <college of the University of Cambridge> the <University of Cambridge> is formed out of colleges
  • has part not used because <college of the University of Cambridge> is not an instance
<Solar System> has parts of the class <inner planet of the Solar System> our <Solar System> has <inner planets> as one of its parts
  • has part not used because <inner planets> is not an instance


References[edit]

  1. https://www.w3.org/TR/rdf-schema/#ch_classes
  2. https://www.w3.org/TR/rdf-schema/#ch_type
  3. https://www.w3.org/TR/rdf-schema/#ch_subclassof
  4. https://www.w3.org/TR/rdf-schema/#ch_subclassof

External links[edit]