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

From: Oliver Ruebenacker <curoli@gmail.com>
Date: Wed, 27 Mar 2013 11:02:24 -0400
Message-ID: <CAA=X4ODR=ubgqL+_xaViHdX0rVXNa-+Jt_PJZ9z3KEFxcFgmFQ@mail.gmail.com>
To: David Booth <david@dbooth.org>
Cc: public-semweb-lifesci@w3.org
     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."

     Take care
     Oliver

On Wed, Mar 27, 2013 at 9:37 AM, David Booth <david@dbooth.org> wrote:
> Hi Oliver,
>
> On 03/25/2013 04:02 PM, Oliver Ruebenacker wrote:
>>
>>       Hello David,
>>
>>    We agree that there are different interpretations. But you haven't
>> shown that the boundaries between interpretations are graphs
>> boundaries (others, including me, think that each interpretation is
>> global).
>
>
> I don't know what you mean by "boundaries between interpretations".
> An interpretation may be applied to any graph or statement to determine its
> truth value (or to a URI to determine the resource to which it is bound in
> that interpretation).
>
> The notion of a graph boundary is purely a matter of convenience and
> utility.  A graph can consist of *any* set of RDF triples.  If you wanted,
> you could apply an interpretation to a graph consisting of three randomly
> selected triples from each RDF document on the web, but it probably wouldn't
> be very useful to do so, because you probably would not care about the truth
> value of that graph.  We generally only apply an interpretation to a graph
> whose truth value we care about.
>
> An interpretation corresponds to the *use* of a graph.  Suppose I have a
> graph that "ambiguously" uses the same URI to denote both a toucan and its
> web page, without asserting that toucans cannot be web pages:
>
>    @prefix : <http://example/>
>    :tweety a :Toucan .
>    :tweety a :WebPage .
>
> When a conforming RDF application takes that RDF graph as input, assumes it
> is true, and produces some output such as "Tweety is a toucan", in effect
> the application has chosen a particular interpretation to apply to that
> graph.  In effect, the choice of interpretation causes the app to produce
> that particular output.  For example, the app might categorize animals into
> species, choosing an interpretation that maps :tweety to a kind of bird.
> But a different conforming RDF application that only cares about web page
> authorship might take that *same* RDF graph as input and choose a different
> interpretation that maps :tweety to a web page, instead outputting "Tweety
> is a web page".  In effect, the app has chosen an interpretation that is
> appropriate for its purpose.
>
> If the graph had also asserted :Toucan owl:disjointWith :WebPage, then the
> graph cannot be true under OWL semantics, and the graph (as is) would be
> unusable to both apps.
>
>>
>>    That makes me wonder whether you consider it in conformance with the
>> specs to choose different boundaries?
>>
>>    For example, would you consider it conforming to apply a different
>> interpretation to each statement? Or how about a different
>> interpretation for each node of a statement? Do you see anything in
>> the specs against doing so?
>
>
> Sure it is in conformance with the spec.  An interpretation can be applied
> to any graph or any RDF statement.  And certainly you could determine the
> truth value of N different statements according to N different
> interpretations.  But would it be useful to do so?  Probably not.
> Furthermore, if two statements are true under two different interpretations,
> that would not tell you whether a graph consisting of those two statements
> would be true under a single interpretation.
>
> OTOH, it *is* useful to apply different intepretations to different graphs,
> and one reason is that you may be using those graphs for different
> applications, each app in effect applying its own interpretation.  But the
> fact that those graphs may be true under different interpretations does
> *not* tell you whether the merge of those graphs will be true under a single
> interpretation.
>
> The RDF Semantics spec only tells you how to compute the truth value of one
> <interpretation, graph> pair at a time, but you can certainly apply it to as
> many <interpretation, graph> pairs as you want -- in full conformance with
> the intent of the spec.  This is the same as if I define a function f of two
> arguments, such that f(x,y) = x+y, that function definition only tells you
> how to compute f(x,y) for one pair of numbers at a time, but you can
> certainly apply it to as many pairs as you want, without in any way
> violating the intent of f's definition.
>
> David



-- 
IT Project Lead at PanGenX (http://www.pangenx.com)
The purpose is always improvement
Received on Wednesday, 27 March 2013 15:02:55 UTC

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