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Re: rdf inclusions (was Re: DAML Level of Effort for FY03-FY05)

From: Frank Manola <fmanola@mitre.org>
Date: Sun, 21 Apr 2002 17:45:03 -0400
Message-ID: <3CC332DF.5000804@mitre.org>
To: Sandro Hawke <sandro@w3.org>
CC: Drew McDermott <drew.mcdermott@yale.edu>, drager@bbn.com, www-rdf-logic@w3.org
Sandro Hawke wrote:

>>Is it supposed to be the case that just mentioning an ontology's
>>namespace means that the file uses that ontology? 
> The namespace declaration is just syntactic sugar (it doesn't appear
> in the N-Triples generated, etc), but if we phrase your question
> differently, the point remains important:
>    Does using a term defined by some ontology O in some
>    RDF graph G mean that G is using O?
> I think a "yes" answer would be convenient but wrong in the long run.

I think a "yes" answer is right, but needs to be qualified.  Sandro is 
correct that the namespace declaration is syntactic sugar, but using it 
does mean that a term from that namespace winds up in the generated 
graph (N-triples), as an absolute URI referring to that specific term. 
And if the terms in that namespace are coming from a given ontology, 
this means that the RDF is supposedly using that term in the sense 
defined by that ontology.  So if I write some RDF with an rdf:about 
referring to an instance defined in that ontology, that's the specific 
instance I'm intending to talk about.  And if I use a property that's 
defined in that ontology in that RDF, the meaning of that property 
defined in that ontology is the meaning I'm intending to use.  Of 
course, when I write that RDF I may have wrongly interpreted the 
meanings of those terms, but that's always going to be a possibility. 
In any event, I think this means that when I use a term defined by some 
ontology O in some RDF graph G, then G is certainly "using" O.  However, 
it may not be using *all* of it.

The rest of Sandro's comment below goes a bit further in discussing what 
"using" might mean.  In the simple examples I'm thinking of, I could be 
using some terms that are defined in an ontology, but even if I'm using 
them correctly, I may not necessarily be commiting to the entire 
ontology (e.g., I may think they got part of it wrong).  Part of this 
has to do with the way the ontology is constructed (e.g., the extent to 
which using any part of the ontology requires effectively commiting to 
other parts).  We do need to think more about what being "based on an 
ontology" means.


> I think this is a special case of broader RDF question:
>    Does using a term T in RDF graph G mean that the author
>    of G believes and and all other RDF graphs which use T?  (obviously
>    not....)    ... that the author of G believes some graph which
>    "defines" T?  (maybe, if we could figure out what "defining"
>    meant; is that what you get when you try to GET from the namespace
>    address?)
> My working answer is this:  when you're looking at a graph G and you
> come across a term T...
>    1.  Other graphs which contain T may have relevant information,
>        but you can't assume the author of G knew about them or
>        believes in them.  If you have your own reasons to trust both
>        them and the author of G, you should use the merged graph.
>    2.  The author of G should be able to state a belief of some 
>        other graph, of which the ontology O is a special case.  This
>        is something like daml:includes, but more general.  Something
>        like "<http://address.of.some.RDF.content> rdf:type
>        rx:TruePage."
>    3.  EricP (and SOAP) keep saying they want "must-understand"
>        messages, which is relevant here, because you might want to say
>        "you must subscribe to O before looking at my message; if you
>        don't then you'll understand my message incorrectly".   I don't
>        have a use case for this, but I do have solution, which is that
>        you provide your graph in the form "if O then G", so the reader
>        must understand both your "if...then" vocabulary and O before
>        it even sees G.
> I know we're working in some different areas, but I hope this still
> made some sense.
>     -- sandro

Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Sunday, 21 April 2002 17:34:39 UTC

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