Wikidata:WikiProject Ontology/Mapping

Wikidata entries (Q and P) have relationships with external ontologies. The typical example is the external identifier, to authority control, but there are many others, not for control but for "linking ontologies", (see wd/sc reports):

(any) entry mapped using exact match P2888;
External-ontology type mapped using external equivalent class P1709;
External-ontology property mapped using external equivalent property P1628;
External-ontology entry mapped using external super-property P2235;
External-ontology entry mapped using external sub-property P2236;
... others?

This guidelines aim to resolve the problem of diversity (some relationships are relevant and other are drafts) and ambiguity (some relationships are similar and need some kind of "rule for choice").

PS: others perhaps need to be created,

... External-ontology property mappeed just like P1629 (but swapped), a kind of "the external-property is subject of this wikidata-type" (operator external property equivalent-subject)...

General guidelines[edit]

...

When to use external ID[edit]

... see Help:Data_type#external-id and Wikidata:List of properties/Generic#Authority control ...

When to use external equivalence and similars[edit]

...

Specific cases[edit]

Some relevant cases in use at Wikidata, sort by "relevance" as LOV statistics.

To check the Wikidata-use, a simple query can be submited to query.wikidata.org. Example:

SELECT * WHERE {  
       {?p wdt:P2235 ?s.}
       UNION { ?p wdt:P2236 ?s. }
       UNION { ?p wdt:P1628 ?s. }
       UNION { ?p wdt:P1709 ?s. }
       UNION { ?p wdt:P2888 ?s. }
       FILTER( REGEX(STR(?s), "purl.org/dc") )
} LIMIT 100

dcterms case[edit]

dcterms classes, properties and datatypes are defined by http://purl.org/dc/terms/ (sometimes dublincore.org/documents/dcmi-terms)

...

skos case[edit]

skos classes and properties are defined at https://www.w3.org/TR/skos-reference/

...

schema case[edit]

schema classes and properties are defined at http://schema.org/

See at this quering and report article (schemaorg/Issue-280, quering Wikidata) all details.

Schema.org entries (types or properties) mapped using Exact Match (P2888);

Schema.org types mapped using (external) Equivalent Class (P1709);

Schema.org properties mapped using (external) Equivalent Property (P1628);

When there's no equivalent but there is a sub/super available, then it (Schema.org properties or types) will be mapped using:
- (external) Super-property (P2235);
- (external) Sub-property (P2236).

... check also Wikidata:Property_proposal/Schema.org_ID (proposal for a Schema.org ID)

Problem: when to use exact match (P2888) or equivalent entry (P1709 or P1628)? In the property cases, how to decide if it is Super or Sub (and not exact or equivalent)?

Best practices: use both, equivalent entry as minimal (for exact or approximate), and exact match only when it is "exact".
New problem: there are no objective criteria to decide what is "approximated" and what is "exact". Use Super/Sub only in obvious/consensual cases.