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Re: owl:sameAs - Is it used in a right way?

From: David Booth <david@dbooth.org>
Date: Thu, 28 Mar 2013 08:51:46 -0400
Message-ID: <51543CE2.7090708@dbooth.org>
To: Oliver Ruebenacker <curoli@gmail.com>
CC: public-semweb-lifesci@w3.org
On 03/27/2013 11:02 AM, Oliver Ruebenacker wrote:
>       Hello David,
>
>    So if I understand your view correctly, then it could be expressed
> in a language close to yours as:
>
>    "Some people believe that if a URI occurs twice within a graph or
> statement, it refers to the same thing. But this is a myth! RDF never
> guarantees that two occurrences of the same URI mean the same thing."

No, that's not correct.  If you are talking about what the URI means 
**within that graph**, then:

   - For any interpretation, every occurrence of that URI in that graph 
refers to the same thing; BUT . . .

   - Different interpretations can be applied to that graph, such that 
the URI means one thing in one interpretation, but means something 
different in another interpretation.

                		  -----------

It all comes down to the fact that, in essence, the RDF Semantics spec 
defines a function -- call it RS -- of *two* arguments: one 
interpretation and one graph (or a piece of a graph, but that's an 
unimportant detail).  You can apply this function to determine the truth 
value of any <interpretation, graph> pair.  If Interpretations is the 
set of all RDF interpretations, and Graphs is the set of all RDF graphs, 
then RS can be defined as:

   RS: (Interpretations x Graphs) -> {true, false}

   For any I in Interpretations and G in Graphs, RS(I, G) is true
   iff the RDF Semantics specification says that G is true under
   interpretation I.

Given RS, we can then define another function -- call it SI -- that 
determines the set of satisfying interpretations for a graph, i.e., the 
set of interpretations under which that graph would be true:

   SI: Graphs -> PowerSet(Interpretations)

   For any G in Graphs, SI(G) = {i in Interpretations | RS(i, G) }

Since the set of satisfying interpretations differs depending on the 
graph, to do anything useful with the RDF Semantics, the key question 
that you must first ask is: **What graph do you wish to consider?** 
Once you have answered that question, you can do useful things, like 
determining the set of satisfying interpretations, or inputting that 
graph to an app that applies its chosen interpretation to it.

David
Received on Thursday, 28 March 2013 12:52:14 UTC

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