Many people have stated that owl:sameAs is problematic because it is being (ab)used without regard for its strong semantics.

SKOS defines the following:

  • skos:closeMatch
  • skos:exactMatch
  • skos:broadMatch
  • skos:narrowMatch
  • skos:relatedMatch

These seem useful and could be a basis for replacing owl:sameAs but what other predicates should exist?

Note: this is not the same question as http://www.semanticoverflow.com/questions/312/mapping-ontologies-are-there-alternatives-to-owlsameas since that is about ontology mapping and my question is about instance data.

asked 27 Jun '10, 02:27

Ian%20Davis's gravatar image

Ian Davis
accept rate: 13%

I don't know if it's a problem, but the SKOS mapping relations ultimately extend skos:semanticRelation, which defines the rdfs:domain and rdfs:range to be skos:Concept. So if this pattern of linking with skos mapping properties were to catch on anyone doing inferencing across linked data would end up with a lot of skos:Concepts.

skos:Concepts all the way down? :-)

I don't necessarily see this as a bad thing, given that a skos:Concept is "an idea or notion; a unit of thought", which IMHO includes pretty much anything. Isn't Linked Data all about our ideas and thoughts about the world anyhow?

I think skos:closeMatch would be a good one to encourage, since it isn't transitive (like skos:exactMatch) and would lead to less semantic drift in linked data.

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answered 27 Jun '10, 11:41

Ed%20Summers's gravatar image

Ed Summers
accept rate: 10%

edited 27 Jun '10, 11:48


I think any linking/identity vocabulary would be superproperties of the skos ones

(27 Jun '10, 14:32) Ian Davis Ian%20Davis's gravatar image

Personally I think link:uri (One of possibly many URIs which identify something.) covers many use cases; rdfs:seeAlso covers another large proportion, and finally owl:sameAs is useful when you want the strong semantics - can't find a use case which isn't covered by these three.

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answered 27 Jun '10, 12:49

Nathan's gravatar image

accept rate: 5%


The comment in the ontology for link:uri says explicitly that it is not meant as an identifier... "The URI requested in this access. This is NOT the relationship betwen a URI and a thing t identifiers"

(07 Jan '13, 14:28) Lin Clark Lin%20Clark's gravatar image

An alternative to owl:sameAs, perhaps a more generic term without the strong semantics, would be a good thing to have.

However the problem with the SKOS properties is that they are quite subjective: how "close" does something have to be before its "exact"ly the same? My view is that these refinements don't really add a great deal in practical terms. The distinctions may be useful in specific application scenarios like SKOS where some specific guidance can be given, but I'm not sure this scales particularly well outside of a community.

I think there's more mileage in providing people with the tools to choose amongst difference views of equivalence. The best way to do that is to start factoring out equivalence links into separate link-sets.

If we are to explore less strong forms of equivalence, then I'd like to see usage patterns such as:

  • rdfs:seeAlso -- for referring to relevant/related RDF data. This fulfills the "RDF hyperlinking" use case without having any strong ontological commitment. It can be specialised for specific linking use cases
  • ex:peer -- identify a "peer" resource in another dataset. This could either be a specialisation of rdfs:seeAlso, or a generalisation of owl:sameAs but without the same semantics
  • owl:sameAs -- as currently used

My feeling that most current deployments actually identify "peer" resources in other datasets rather than items that are absolutely identical. The "peer" relationship would still allow linking and navigation between datasets, but still let applications treat the resources as identical if necessary, e.g. by application of local rules.

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answered 12 Jul '10, 11:46

ldodds's gravatar image

accept rate: 32%

I found "When owl:sameAs isn’t the Same" a great summary of the problem. Section 5 lays out some varieties of same-ness.

As for some examples:


With respect to their class-ness / property-ness they can be substituted, but not generally. Is this an instance of 'Same Thing As But Referentially Opaque'? Skos is similar, although weaker since it's not apparent when substitution is possible.

og:sameAs (proposal)

The idea here is two things are talking about the same thing. I think the idea is ?x og:same ?y would entail ?x foaf:primaryTopic ?p . ?y foaf:primaryTopic ?p. The IMDB page about the Godfather is the same as the Godfather Wikipedia page.


Related to the previous, if I understand correctly Hayes and Halpin would grant a variety of same-ness here, in that one thing can stand in for another (such as an IMDB page for the film itself).

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answered 27 Jun '10, 15:51

Comment%20Bot's gravatar image

Comment Bot
accept rate: 42%

The needs differ for generic classes/properties and instances. We've been working [1] on the problem of recognizing that two RDF instances are intended to refer to the same object in the world -- e.g. that two foaf:Persons describe the same person. In some ways the problem conceptually is simpler -- there may be universal consensus that the "D. Knuth" cited as the author of one paper is the same individual as the "Donald E. Knuth" in another. But asserting owl:sameAs between the two foaf:Person instances can be problematic [2].

The solution we are currently exploring is to define a new property to assert that two RDF instances are co-referential when they are believed to describe the same object in the world. The two RDF descriptions might be incompatible because they are true at different times, or the sources disagree about some of the facts, or any number of reasons, so merging them with owl:sameAs may lead to contradictions. However, virtually merging the descriptions in a co-reference engine is fine -- both provide information that is useful in disambiguating future references as well as for many other purposes.

Our property (:coref) is a transitive, symmetric property that is a super-property of owl:sameAs and is paired with another, :notCoref that is symmetric and generalizes owl:differentFrom.

[1] http://ebiquity.umbc.edu/paper/html/id/471/

[2] http://ebiquity.umbc.edu/paper/html/id/473/

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answered 30 Jun '10, 16:14

Tim%20Finin's gravatar image

Tim Finin
accept rate: 25%

edited 30 Jun '10, 17:32

Depends on what you're trying to express, in what context.

By which I mean to challenge the idea that, as phrased in generality, the question is even important. In an actual context or use, as opposed to the abstract, it's usually easy to see what the proper relationship is. In my World Cup dataset, for example, the relationship from a Match to a dbpedia URI is "Link". E.g., this. For that data, that makes sense.

It doesn't really matter whether it's a standard predicate or not. The beauty of owl:sameAs (and owl:equivalentProperty) is that they can be used later, by some other user of the data in some other context, to fix up the semantics as necessary for that use. If my "Link" needs to be treated as "owl:sameAs" for your reasoner to hook up some of my stuff with some dbpedia stuff, then fine. In your dataset, which you combine on your servers with mine and dbpedia's, you can say:

ndl:matchLink owl:equivalentProperty owl:sameAs .
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answered 27 Jun '10, 03:01

glenn%20mcdonald's gravatar image

glenn mcdonald
accept rate: 15%

edited 28 Jun '10, 13:15

that two URIs denote the same thing, or a similar thing, or things that might be the same for some purposes etc.

(27 Jun '10, 04:58) Ian Davis Ian%20Davis's gravatar image

Not enough space in these comments to continue this as a discussion, I see. I've edited the answer above...

(28 Jun '10, 01:19) glenn mcdonald glenn%20mcdonald's gravatar image

There is no such thing as owl:samePropertyAs. Do you mean owl:equivalentProperty?

(28 Jun '10, 03:58) cygri ♦ cygri's gravatar image

Yes, sorry, looking at an old reference. Fixed. The point is the same.

(28 Jun '10, 13:16) glenn mcdonald glenn%20mcdonald's gravatar image

Another canidate is ore:similarTo from the OAI-ORE vocabulary. The rdfs:domain of this property is ore:Aggregation, but this issue is similar to having rdfs:domain and rdfs:range to be skos:Concept.

An ore:Aggregation is "A set of related resources (Aggregated Resources), grouped together such that the set can be treated as a single resource". The OAI-ORE data model defines: "Aggregation is a Resource of type ore:Aggregation that is a set of other Resources". In detail, ore:Aggregation is a subclass of dcmitype:Collection, which is "an aggregation of items. The term collection means that the resource is described as a group; its parts may be separately described and navigated."

Ed Summers argued that in the end skos:Concept includes pretty much anything. So could ore:Aggregation, as long as you can split of the thing into smaller parts.

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answered 06 Sep '11, 17:11

Jakob's gravatar image

accept rate: 10%

owl:sameAs is frequently used when people want to link linked data, it's common to say

dbpedia:Brussels owl:sameAs someOtherDatabase:Brussels_BE .

The trouble is that owl:sameAs, interpreted conventionally, is too powerful. Any reasoner that supports owl:sameAs can be trashed by adding a single owl:sameAs statement to the T-Box. Even in the A-Box, owl:sameAs can cause errors that cascade, causing the identities of important topics to become confused.

To do better, it's necessary to reify subjects, in the sense that you take responsibility for them. You don't store

dbpedia:Brussels dbpedia-owl:postalCode "BE-BRU" .

but instead you store

myIdentifier:t7312 myPredicate:postalCode "BE-BRU".

Now, in your system you need to keep track of how your identifiers map to other identifiers -- so you know which identifiers you should accept (wikipedia redirects) and also which identifiers you should publish (the one that we believe is the most official.) This system is a burden to maintain, but you need it if you're maintaining a specific point-of-view about what things exist. You'll need to do that if you want to get precision and recall higher than a certain level.

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answered 08 Sep '11, 11:10

database_animal's gravatar image

database_animal ♦
accept rate: 15%

"Overloading OWL sameAs" is a nice summary and link collection of owl:sameAs related thoughts (created by Michael Uschold).

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answered 10 Sep '11, 08:28

zazi's gravatar image

accept rate: 13%

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question asked: 27 Jun '10, 02:27

question was seen: 9,379 times

last updated: 07 Jan '13, 14:28