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Re: What's the difference? rdf:about, owl:sameIndividualAs

From: Thomas B. Passin <tpassin@comcast.net>
Date: Sun, 25 May 2003 16:53:58 -0400
To: www-rdf-logic@w3.org
Message-id: <005e01c322ff$c3ac9c20$6401a8c0@tbp1>

[Jimmy Cerra]

> What's the difference between rdf:about and owl:sameIndividualAs?  They
> all seem to be used to define a resource.

From both a formal and a modeling point of view, they are very different.
rdf:about is a syntactical device to identify the subject of a triple in a
serialized RDF graph.  owl:sameIndividualAs is a predicate, used as part of
a triple to assert a statement.  Whether or not you think that kind of
assertion is always sensible to make is another thing althogether.

Take the following example:
> <owl:Thing rdf:about="uri#foo" />
> That serialized RDF statement says that a resource, identified by
> "uri#foo", is an individual (as defined by OWL).

It can be any resource.  It could be a class.  Right, it has the effect of
an empty statement about uri#foo.

 However, I could also
> say that a blank node that is identical to the resource identified by
> "uri#foo" is an individual:

> <owl:Thing>
> <owl:sameIndividualAs rdf:resource="uri#foo" />
> </owl:Thing>
> From that statement, an agent should conclude that the resource
> identified by "uri#foo" has the same properties as that blank node.

You just asserted that owlThing, a predefined class, is the same as uri#foo.
From that, if I do not know anything else about uri#foo, I could infer that
the node uri#foo is the same node as the node representing &owl;#Thing (or
whatever the right URI is)

> Since the blank node is an individual,

We only knew it is a Resource...

> then the resource identified by
> "uri#foo" must have the same properties - mainly that it is an
> individual.

No, just a Resource.

So rdf:about and owl:sameIndividualAs can be used to
> identify a resource; the former by direct statements and the latter by
> inference.

There are many ways to identify resources by inference.  That does not mean
that all statements that feed those inference are equivalent.  Anyway,
rdf:about  is not a resource or property, so they are not equivalent.
Besides that, the sense in which rdf:about "identifies" a resource is very
different - it indicates in the serialization which node to construct or to
attach an arc to.  The predicates represent, of course, the arcs themselves.
So there is no way the two are the "same thing" or equivalent.  One is a
construction device, one is a part of a graph.


Tom P
Received on Sunday, 25 May 2003 16:52:16 UTC

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