When owl:sameAs isn't the Same

Harry Halpin and Pat Hayes, <hhalpin@w3.org and phayes@ihmc.us>


LDOW 2010, Raleigh, March 2010


The built-in OWL property owl:sameAs links an individual to an individual and Such an owl:sameAs statement indicates that two URI references actually refer to the same thing: the individuals have the same identity (from OWL spec)

It's symmetric and transitive

Anyone can link to your data-set with owl:sameAs from anywhere else on the Web without your permission, and any statement they make about their own URI will immediately apply to yours!

Same Thing As But Different Context

Eiffel Tower 

rdf:sameInContext: Two URIs do refer to the same thing and all properties do hold of both URIs, but that we cannot re-use the URI in a different context.

Example: Lynn Stein, when at a meeting of the PTA (Parent-Teacher Association) she is Ms. Stein, Rachel's mum, not Professor Stein of MIT. This does not mean that in the PTA meeting Ms. Stein is somehow not a professor, but that within that context those properties do not matter.

Same Thing As But Referentially Opaque

Gottlob Frege

rdf:sameName: When the two URIs do refer to the same thing, but all the properties ascribed to one URI are not necessarily accepted by the other.

Example: The concept of sodium in DBpedia, which has an owl:sameAs link to the concept of sodium in OpenCyc. The OpenCyc ontology says that an element is the set (class) of all pieces of the pure element, so that for example sodium in Cyc has a member which is the lump of pure metallic sodium. On the other hand, sodium as defined by DBPedia is used to also include isotopes, which have different number of neutrons than standard sodium.


Eiffel Tower 

rdf:represents: Just as a picture of something depicts something, a URI can be for a representation of a thing rather than the thing itself.

Example:Using a web-page, an e-mail address, or a picture of Berners-Lee to refer to Tim Berners-Lee himself, using something accidentally or contextually to refer to something, a phenomenon called displaced reference.

Very Similar To

Photo of Eiffel

rdf:similarTo: two things are not identical but simply closely related in some manner.

Example:This, for example, is the relationship between the district of Paris and the Department of Paris in Cyc. The relationship between isotopes and elements, the quantity and a measurement of a quantity, and an image and a facsimile of that image.

(RDF) Next Steps!

Pat Hayes

  1. Can we formalize these using a formal semantics of named graphs? I.e. that a statement only holds within a named graph or set of named graphs?
  2. How reliable all these distinctions?
  3. Can we do data-driven spec development for the next generation of the Semantic Web?
  4. Are there more distinctions we are not aware of?