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Help:Basic membership properties

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This page in a nutshell:

Instances are individuals or single things
A class is an abstract collection of instances
Each Wikidata item is an instance or a class or both

Introduction

This page explains the differences among the propertiesinstance of(P31),subclass of(P279) andpart of(P361).

Definitions

To understand the differences, it is important to be familiar with the termsinstance andclass. A class is an abstraction that describes a set (or collection) of things, called its instances. Typically, all the instances belonging to a class share a set of properties, which properties characterize the class.

If all the instances of class A necessarily also belong to class B, then we say A is asubclass of B.

Examples

classhuman(Q5) with instancesAbraham Lincoln(Q91),Mahatma Gandhi(Q1001),Isaac Newton(Q935), etc.
classlighthouse(Q39715) with instancesAmrum Lighthouse(Q20669),Lighthouse of Alexandria(Q43244), etc.
classocean(Q9430) with instancesAtlantic Ocean(Q97),Pacific Ocean(Q98), etc.
classpublic election(Q40231) with instance2016 Taiwanese presidential election(Q20683626), etc.

Practical aspects

Anitem can be both an instance and a class. An item is an instance if it has aninstance of(P31) property. An item is a class if it is the value associated with some other item'sinstance of(P31) property (or if it has asubclass of(P279) property). For example,Angela Merkel(Q567) is an instance ofpolitician(Q82955), andpolitician(Q82955) is an instance ofprofession(Q28640). So the itempolitician(Q82955) is both a class and an instance.
The complete set of instances implied by a class might or might not exist as items within Wikidata.
Typically, a class is characterized by a set of properties shared by all instances. The instances differ from each other in the values they have for those properties, but not in the fact of having the properties themselves (although this is not enforced by Wikidata).

instance of(P31)

The relation between instances with a common feature and a class characterized by this feature is produced with the propertyinstance of(P31).We useinstance of(P31) instead ofsubclass of(P279) when we cannot say anything about instances with such relation. More specifically, it is anrdf:type.^[1]

For example,Atlantic Ocean(Q97) andPacific Ocean(Q98) are both instances ofocean(Q9430). We write therefore on Wikidata:

subclass of(P279)

Is used to state thatall the instances of one class are instances of another^[2]
More specifically, it is anrdfs:subClassOf^[3]‎
Ifany instances of the subject class arenot instances of the value class,subclass of(P279) is not appropriate.partially coincident with(P1382) may be used to link overlapping classes where neither is a strict subclass of the other.

Several examples:

Another example:

classlake(Q23397) with instancesLake Baikal(Q5513) andLake Erie(Q5492);
classocean(Q9430) with instancesAtlantic Ocean(Q97) andPacific Ocean(Q98).

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

NowLake Baikal(Q5513),Lake Erie(Q5492),Atlantic Ocean(Q97) andPacific Ocean(Q98) will all betransitive (indirect) instances ofbody of water(Q15324). In general wecan use more abstract objects (likebody of water(Q15324)) instead of enumerations (lake(Q23397) andocean(Q9430)) both: 1. in our statements and 2. in our questions (not covered at this help page).

Transitive properties

The propertysubclass of(P279) is atransitive Wikidata property(Q18647515). This means: if a class A is a subclass of class B, and B is a subclass of class C, then A is implicitly also a subclass of C.There is then no general need to add an explicit statement to Wikidata declaring A to be a subclass of C.

For example,tree(Q10884) is a subclass ofwoody plant(Q757163), andwoody plant(Q757163) is a subclass ofplant(Q756). Thustree(Q10884) is implicitly also a subclass ofplant(Q756).

Similarly, if item x is an instance of class B, and B is a subclass of class C, then x is implicitly also an instance of C. There is then no general need to add an explicit statement to Wikidata declaring x to be an instance of C.

For example,Lighthouse of Alexandria(Q43244) is an instance oflighthouse(Q39715) andlighthouse(Q39715) is a subclass oftower(Q12518).Lighthouse of Alexandria(Q43244) is thus an instance oftower(Q12518).

The propertyinstance of(P31) isnot transitive. Considering the example from above:Angela Merkel(Q567) is an instance ofpolitician(Q82955), andpolitician(Q82955) is an instance ofprofession(Q28640), but it would be incorrect to say thatAngela Merkel(Q567) is an instance ofprofession(Q28640).

Inferences based on transitivity do not takequalifiers into account, soinstance of(P31) andsubclass of(P279) statements must be valid while ignoring any qualifiers; in other words, these statements should not have anyrestrictive qualifier(Q61719275), or any qualifier that is being used restrictively. For example, if A is often, but not always, a subclass of B, then it is not valid to state that A is a subclass of B withnature of statement(P5102) =often(Q28962312), because this will lead to false inferences.

part of(P361)

Items cannot be an instance of another non-class, but they can be part of another non-class. For example,Albert Einstein's brain(Q2464312) is a part ofAlbert Einstein(Q937). On Wikidata we usepart of(P361) for this relation.

Albert Einstein's brain(Q2464312)part of(P361)Albert Einstein(Q937).

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

human brain(Q492038)part of(P361)Homo sapiens(Q15978631).

The use ofinstance of(P31) instead ofpart of(P361) would be wrong here becausehuman brain(Q492038) is not a person. Usingsubclass of(P279) would also be wrong because an instance ofhuman brain(Q492038) (e.g.Albert Einstein's brain(Q2464312)) is not an instance of the classHomo sapiens(Q15978631).

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

Inverse relations ofpart of(P361)

has part(s)(P527) - is used to say that an instance has as part some other instance or that instances of a class have as part an instance of some other class
has part(s) of the class(P2670) - is used to say that an instance (never a class) has as part an instance of a class. If the parent item is both an instance and a class,has part(s) of the class(P2670) should not be used.

For example,

Greek alphabet(Q8216)has part(s)(P527)Α(Q9887) (instance-instance)
alphabet(Q9779)has part(s)(P527)letter(Q9788) (class-class)
Greek alphabet(Q8216)has part(s) of the class(P2670)Greek letter(Q19793459) (instance-class)

In the first example,has part(s)(P527) is used becauseGreek alphabet(Q8216) has as partΑ(Q9887).has part(s)(P527) is also used in the second example because instances ofalphabet(Q9779) have instances ofletter(Q9788) as parts. In the last example, we takehas part(s) of the class(P2670) sinceGreek alphabet(Q8216) has one or more instances ofGreek letter(Q19793459) as parts.

Examples

instance of(P31) vs.subclass of(P279) vs.part of(P361)

Differences amonginstance of(P31),subclass of(P279) andpart 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>	<USSNimitz> is a single concrete aircraft carrier, <supercarrier> is an aircraft carrier class which has many instances (aircraft carriers)	subclass of not used because <USSNimitz> is not a class part of not used because <USSNimitz> 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 forinstance 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. <USSNimitz>) cannot be part of an instance of aircraft carrier (e.g. <USSEnterprise>)
				<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>	<USSNimitz> is a concrete aircraft carrier, <CSG-11> is a concrete carrier strike group, <USSNimitz> 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 USSNimitz>, can be an instance) subclass of not used because an instance of the former (e.g. <flight deck of USSNimitz>) cannot be the same thing as an instance of the latter (e.g. <USSNimitz>)
				<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>
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>").

has part(s)(P527) vs.has part(s) of the class(P2670)

Here is a table that explains the difference betweenhas part(s)(P527) andhas part(s) of the class(P2670).

has part(s)(P527) should be used for class-class and instance-instance relationships.

has part(s) of the class(P2670) should be used for instance-class relationships.If you see a constraint violation on an item withhas part(s) of the class(P2670)...

If the item is a class and hassubclass of(P279), it should usehas part(s)(P527) instead ofhas part(s) of the class(P2670), even if it also hasinstance of(P31).
The item may wrongly be a class and should instead be an instance. Removesubclass of(P279) and make sure it has a properinstance of(P31).

Differences amonghas part(s)(P527) andhas part(s) of the class(P2670)
Property	X	Y	what it denotes	example	explanation	why not use…
<X>has part(s) <Y>	instance	instance	instance X has instance Y among its parts or components	<United States Congress>has part(s) <United States Senate>	the US Congress has two parts, the House of Representatives and the Senate	has part(s) of the class not used because <United States Congress> and <United States Senate> are concrete objects
	instance	instance	instance X has instance Y among its parts or components	<Solar System>has part(s) <Mars>	<Mars> is one of the planets in the <Solar System>	has part(s) of the class not used because <Solar System> and <Mars> are concrete objects
	class	class	an instance of X has an instance of Y among its parts or components	<body>has part(s) <head>	in general a <body> (anatomical feature) has a <head> as one of its parts	has part(s) of the class not used because <body> and <head> are both classes
	class	class		<galaxy>has part(s) <star>	a <galaxy> has <stars> as one of its parts	has part(s) of the class not used because <galaxy> and <star> are both classes
<X>has part(s) of the class <Y>	instance	class	the specific item X include some instance of class Y among its parts or components	<University of Cambridge>has part(s) of the class <college of the University of Cambridge>	the <University of Cambridge> has colleges as parts	has part(s) not used because <University of Cambridge> does not have the class <college of the University of Cambridge> as a part, but instead has colleges as parts
				<Solar System>has part(s) of the class <inner planet of the Solar System>	our <Solar System> has one or more <inner planets> in its parts	has part(s) not used because <Solar System> does not have the class of <inner planets> as a part, but instead has planets as parts
				<Albert Einstein>has part(s) of the class <human brain>	<Albert Einstein> had a <human brain> as a part	has part(s) not used because <human brain> is a class, not an instance, even if he had just one.

Queries

Wikidata Queries can be used to find members of a given class, for exampleall subclasses of "Literary Work"; aWikidata Query Builder is available to help.

navbox

v t e Wikidata properties related totree(Q223655)

This template lists some major properties which can be used to digitizingtree-shaped data. For techniques about creating tree, seeHelp:Tree

↕Vertical relations↕	subclass of instance of part of/has part(s) follows/followed by replaces/replaced by connects with union of/disjoint union of broader concept including has part(s) of the class Person:father mother stepparent godparent child Anatomy:anatomical location anatomical branch of/has anatomical branch presynaptic connection/postsynaptic connection Astronomy:located on astronomical body/parent astronomical body/child astronomical body Geography:underlies/overlies tributary/distributary origin of the watercourse/outflows next crossing upstream/next crossing downstream structure replaces/structure replaced by adjacent building Language:dialect of Occurrence:has cause/has effect has immediate cause/immediate cause of has contributing factor/contributing factor of Organization:separated from parent organization/has subsidiary owned by/owner of next higher rank/next lower rank league level above/league level below Art & Research:student of/student doctoral advisor/doctoral student based on/derivative work inspired by/influenced by cites work reply to Taxonomy:parent taxon Wikimedia:subproperty of category contains

↔Horizontal relations↔	said to be the same as permanent duplicated item partially coincident with different from narrower external class Person:spouse unmarried partner sibling relative Genetics:ortholog Anatomy:sexually homologous with Astronomy:companion of Taxonomy:taxon synonym taxon common name replaced synonym (for nom. nov.) Wikimedia:inverse property

Other	is metaclass for(P8225) metasubclass of(P2445) transitive over(P6609)

Items	umbrella term(Q210588) hypernym(Q609507) empty class(Q128139417) the empty class(Q126726396) individual item(Q132907471)

Wikimedia template	`{{Tree}}` `{{Wikidata/FamilyTree}}` `{{Family tree}}` `{{Parent taxon tree}}` Module:Haplogroup `{{Item classification}}` `{{SuperclassTree}}`

Related property:Wikidata:WikiProject Ontology -Wikidata:WikiProject Genealogy -Help:Basic membership properties -Help:Modeling causes -Help:Tree

References

External links

Multi-Level Conceptual Modeling: Theory and Applications — explains differences betweeninstance of(P31) andsubclass of(P279) under the conceptual framework of multi-level conceptual modelling. Skip to part 4 for Wikidata-related content.