Equivalence Links

How do we indicate that different URIs refer to the same resource or concept?


Linked Data is published in a de-centralised way with multiple people and organisations collectively publishing data about the same resources. While it is a goal to reuse identifiers wherever possible this may not always be achievable. If data has been published in this way, how can links be built between datasets in order to identify that distinct URIs refer to the same resource?


Use owl:sameAs, skos:exactMatch, or similar specialised relation, to indicate that two URIs are equivalent.


#Statement from Data Set 1
ex:bob a foaf:Person.

#Statement from Data Set 2, with equivalence
ex:otherBob a foaf:Person.
ex:otherBob owl:sameAs ex:bob.


Distributed publishing is a fact of life on the web. Semantic web technologies have built-in support for handling distributed publishing of both data and schemas by standardising specific relations for bringing together disparate datasources. The most important of these facilities is the owl:sameAs relation, which indicates that two URIs are equivalent. According to the semantics defined in the OWL standard, the two URIs are synonyms of each other and all statements made about one of those URIs is also considered to be true of the other.

With support from a reasoner the owl:sameAs relation allows a semantic web application to query and interact with a single view across any number of datasets. This allows data to be integrated, without requiring any merging or re-processing of the data. It also avoids the need for up-front convergence on standard identifier schemes.

However owl:sameAs is only one possible equivalence relation that could be stated between resources. Other vocabularies may choose to define additional relationships that have less strong semantics associated with them. For example SKOS defines two additional properties, skos:closeMatch and skos:exactMatch, that can be used to state equivalences between concepts in a thesaurus. The relations allow for more fuzzy notions of equivalence and have weaker semantics: skos:exactMatch declares two concepts to be the same but doesn't imply that all statements about one concept are also true of another.

OWL also defines some additional specialised equivalence relations for relating together classes (owl:equivalentClass) and properties (owl:equivalentProperty). These should be used instead of owl:sameAs when relating together terms in an ontology.