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RE: stating that something doesn't exist

From: Johnson, Matthew C. (LNG-HBE) <Matthew.C.Johnson@lexisnexis.com>
Date: Thu, 22 May 2008 08:42:31 -0400
Message-ID: <0FE5E87C5F0AE84B8C667FDC5224F6DA0229F19C@LNGDAYEXCP01VC.legal.regn.net>
To: "Peter Ansell" <ansell.peter@gmail.com>
Cc: <semantic-web@w3.org>

This discussion is making me think that using SPARQL to [help] answer
the question as to whether a given pub links to another might be the
right way to go.  This brings me back around to questions on the
open-world/closed-world assumption.  But I just put that question in a
response to Alan Ruttenberg's email so I won't ask it again here.



> -----Original Message-----
> From: Peter Ansell [mailto:ansell.peter@gmail.com]
> Sent: Thursday, May 22, 2008 12:14 AM
> To: Johnson, Matthew C. (LNG-HBE)
> Cc: semantic-web@w3.org
> Subject: Re: stating that something doesn't exist
> 
> 2008/5/22 Johnson, Matthew C. (LNG-HBE)
> <Matthew.C.Johnson@lexisnexis.com>:
> > Hmm.  This is interesting, thanks.  As far as generating a lot of
> > triples from a sparsely linking set of publications, I think my
actual
> > use-case would probably eliminate that.  I suspect that this type of
> > query would normally be done on a publication-by-publication basis.
So
> > I would really be checking if any links exist specifically for
> > publication 2 to [specifically] publication 3.  This would
dramatically
> > reduce the number of triples generated (although it might still take
> > some time).
> 
> You can modify this query to specifically insert the two publications
> into the query and it should dramatically improve the performance over
> the all vs all publication because it is still an existence query so
> if the SPARQL engine can utilise a database index against specific
> publications it should have similar performance to a direct SQL query.
> 
> > Also, I suspect another alternative would be to let the application
> > itself do some of the rationalization by simply grabbing all of the
> > publications that "pub 2" does link to (a simple query) and then
> > checking to see if "pub 3" is in that list.  Ideally, I would like
the
> > data or query to say this directly (really, I'd just like a yes or
no
> > answer) but if performance becomes an issue, it might be a second
> > choice.
> 
> I don't think the query would be too inefficient if you know what the
> publications are. I was referring to the all vs all capabilities when
> I said it might not be efficient. Basically if there is a row returned
> then you have a result, or conversely if no rows are returned then you
> have the opposite result.
> 
> Peter
Received on Thursday, 22 May 2008 12:43:16 GMT

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