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RE: Spatial datatypes and RDF/OWL

From: John Goodwin <John.Goodwin@ordnancesurvey.co.uk>
Date: Tue, 15 Apr 2008 11:10:24 +0100
Message-ID: <6A035FEF345E064E893D784097F8BC7F024A1755@OSMAIL.ordsvy.gov.uk>
To: "Dave Kolas" <dkolas@bbn.com>, <semantic-web@w3.org>

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

WHERE{
    ?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 10:11:10 UTC

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