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RE: Subjects as Literals, [was Re: The Ordered List Ontology]

From: Michael Schneider <schneid@fzi.de>
Date: Fri, 2 Jul 2010 14:40:54 +0200
Message-ID: <0EF30CAA69519C4CB91D01481AEA06A001F07C60@judith.fzi.de>
To: "Kingsley Idehen" <kidehen@openlinksw.com>
Cc: "Linked Data community" <public-lod@w3.org>, "Semantic Web" <semantic-web@w3.org>, "Pat Hayes" <phayes@ihmc.us>
Kingsley Idehen wrote:

>So why: Subject-Predicate-Object  (SPO) everywhere re. RDF?
>
>O-R-O reflects what you've just described.
>
>Like many of the RDF oddities (playing out nicely in this thread), you
>have an O-R-O but everyone talks about S-P-O.
>
>"Subject" has implicit meaning, it lends itself to describing stuff.  If
>I recall, RDF stands for: Resource Description Framework.
>
>I guess "Description" also means nothing?

"S-P-O" typically refers to a syntactic aspect of RDF triples, while "O-R-O"
refers to a semantic aspect.

"S-P-O": "S" ("subject") stands for the first node in an RDF triple. "P"
("predicate") for the second node. "O" ("object") for the third node. The
nodes and the triples are entities of the RDF Abstract Syntax. They don't
have any semantic meaning on their own.

"O-R-O": In the RDF semantics, a syntactic RDF triple is interpreted as a
relationship that holds between two individuals. The two "O"s refer the two
individuals (or resources, or objects), being taken from the domain of
discourse (the "world", about which assertions are made). The "R" stands for
the property (or relation; in any case a semantic entity) that is used to
define the relationship between the two individuals. 

So, these are very different aspects that must not be confused. An "S-P-O"
syntactic RDF triple is interpreted as a "O-R-O" semantic relationship
between individuals. The "S" in "S-P-O" can be a URI, a bNode, and maybe
also a literal in the future. The "O"s in "O-R-O" stand for entities in the
"world". A semantic interpretation function can then use the "S" to denote
(to "name") the "O". But there is no a-priory connection between the two:
any "S-P-O" triple can be interpreted by any "O-R-O" relationship.

I think, the main confusion comes from the use of the term "object" for two
entirely different things: In the case of "O-R-O", it refers to (semantic)
individuals. In the case of "S-P-O", it refers to a position in a
(syntactic) RDF triple.

Michael

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Received on Friday, 2 July 2010 12:41:28 UTC

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