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Re: Querying reified statements

From: Libby Miller <Libby.Miller@bristol.ac.uk>
Date: Wed, 13 Dec 2000 13:46:49 +0000 (GMT)
To: Geoff Chappell <geoff@sover.net>
cc: Libby Miller <Libby.Miller@bristol.ac.uk>, David Allsopp <dallsopp@signal.dera.gov.uk>, www-rdf-interest <www-rdf-interest@w3.org>
Message-ID: <Pine.GSO.4.21.0012131334240.7882-100000@mail.ilrt.bris.ac.uk>

Hi Geoff


On Wed, 13 Dec 2000, Geoff Chappell wrote:


> I've been experimenting recently with a query language that takes queries of
> the form:
> 
>     select  ?age where {?x ?y {age JohnSmith ?age}}
> 
> which behind the scenes results in a query:
> 
>     select ?age where {?x ?y ?z} and {rdf:type ?z rdf:Statement} and
> {rdf:subject ?z JohnSmith}
>                 and {rdf:predicate ?z age} and {rdf:object ?z ?age}


That's a nice way of simplifying the syntax for reified queries. I guess 
I was confusing flattening the model somehow with making the syntax
more intuitive for reified statements. This sort of thing would do the
trick for me.

> 
> Similarly, inner triples are assumed to refer to reified statements in
> insert, delete, infer, and other commands. Additional nesting of triples is
> allowed (i.e. he says she says such and such).  This seems to be a pretty
> natural representation and works well in practice.


Sounds great! Are you thinking of making any papers / code public? I'm
very interested in how people are tackling these problems.

thanks,

Libby


> 
> rgds,
> 
> Geoff Chappell
> ----- Original Message -----
> From: "Libby Miller" <Libby.Miller@bristol.ac.uk>
> To: "David Allsopp" <dallsopp@signal.dera.gov.uk>
> Cc: <www-rdf-interest@w3.org>
> Sent: Wednesday, December 13, 2000 7:46 AM
> Subject: Re: Querying reified statements
> 
> 
> >
> >
> > On Wed, 13 Dec 2000, David Allsopp wrote:
> >
> > >
> > > But if I wanted a query along the lines of "What do people say John
> > > Smith's age is?" I would need something like:
> > >
> > >   select ?a where (?x rdf:type Statement)(?x rdf:subject JohnSmith)(?x
> > > rdf:predicate age)(?x rdf:object ?a)
> > >
> > > which even for this trivial example is getting complex.  I'd like a way
> > > of 'drilling down' through reification, possibly through multiple layers
> > > (A says that B says that John Smith is 42...).
> >
> > Hi David,
> >
> > You're right, this is a real nuisance, especially since queries like
> > this also tend to be inefficient, because rdf:type statement,
> > rdf:subject will be very common if you're dealing with a lot of reified
> > statements.
> >
> > >
> > > Perhaps the solution is to 'flatten' an RDF model containing reified
> > > statements (applying filters according to the origin of the statements
> > > or other criteria) to generate a model without any reifications, which
> > > can be queried easily.
> >
> > I was trying to think around this problem, but I haven't bee able to
> > work out how it can be done. If we have
> >
> > [bag1]-- 1 -- [Statement1]
> > --- subject
> > --- predicate
> > --- object
> >
> > there's no obvious way to flatten it, because without reifying the
> > statement there's no way to refer to the statement rather than its
> > constituents. So it looks as if you can't connect parts of the model
> > together unambiguously.
> >
> > I'd be very interested in any ideas you have about how to tackle this.
> >
> > On the plus side though, it does mean that you can have very general
> > queries about a resource if you have lots of reified statements in a
> > database, because e.g.
> >
> >    select ?z, ?a where (?x rdf:type Statement)(?x rdf:subject
> > JohnSmith)(?x rdf:predicate ?z)(?x rdf:object ?a)
> >
> > will get you all the predicate-object pairs with JohnSmith as the
> > subject.
> >
> > cheers,
> >
> >
> > Libby
> 
> 
Received on Wednesday, 13 December 2000 08:47:40 GMT

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