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Re: Spatial datatypes and RDF/OWL

From: Dave Kolas <dkolas@bbn.com>
Date: Tue, 15 Apr 2008 11:07:47 -0400
Message-ID: <4804C4C3.3080905@bbn.com>
To: John Goodwin <John.Goodwin@ordnancesurvey.co.uk>
CC: semantic-web@w3.org


Slightly wrong end of the stick. 

It's actually done at query time.  The only thing that happens at insert 
time is that the point or polygon associated with an entity is indexed.  
While you could do load-time assertions for something like touches, it 
obviously wouldn't work for things like within a buffer distance.  The 
KB just knows some triples are calculable, and calculates them 


John Goodwin wrote:
> Hi Dave,
> Thanks for your reply. Cathy and Glen are colleagues of mine so I ask
> them about your discussion. I would be interested to know how this
> scales. Am I correct in thing you do something like generate a rule
> hasGeom(a,g1) ^ hasGeom(b,g2) ^ TOUCHES(g1,g2) -> borders(a,b)
> where TOUCHES basically takes care of the spatial calculations? In
> otherwords you do the spatial querying on load, and then the rdf simply
> contains assertions of the for "a borders b" which you query with
> standard SPARQL? Or am I getting the wrong end of the stick here?
> John
> -----Original Message-----
> From: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org]
> On Behalf Of Dave Kolas
> Sent: 14 April 2008 19:03
> To: semantic-web@w3.org
> Subject: Re: Spatial datatypes and RDF/OWL
> Hi John, Steve, all:
> Our group at BBN has been doing some work in this space for a while. 
> We have a prototype for combined RDF and spatial storage, a paper on the
> approach is available at [1].
> Our preference is to have the knowledgebase recognize spatial predicate 
> triples and process them appropriately, rather than build functions into
> SPARQL's filter clauses.  This way, SPARQL parsers /engines need not be 
> extended, all of it can be done at a lower level.
> Your query would be written like:
> SELECT ?a ?b
>     ?a hasGeometry ?g1 .
>     ?b hasGeometry ?g2 .
>     ?g1 touches ?g2 .
> }
> So it accomplishes the same thing.  The same works for data insertion; 
> things that look like points or polygons are detected and indexed.
> Another nice thing about this approach is that these relationships can 
> be asserted in an RDF document, for instance if they were being 
> transferred to a KB that couldn't do spatial processing. 
> Right now, the knowledgebase looks for these predicates explicitly; 
> something like triggers might be useful for generalizing this.
> One change that would improve our current prototype would be to replace 
> the memory-based spatial index with a persistent one.  With the 
> in-memory spatial index, there is a clear cap as to the number of 
> spatial entites it can handle.  I actually chatted with Cathy Dolbear 
> and Glen Hart a bit about this before we'd done any of the work. 
> Thanks,
> --Dave--
> [1] 
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Received on Tuesday, 15 April 2008 15:06:25 UTC

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