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RE: RDF IG meeting at W3C Technical Plenary 2001-02-28

From: Dan Brickley <danbri@w3.org>
Date: Tue, 23 Jan 2001 13:26:23 -0500 (EST)
To: "Matola,Tod" <matola@oclc.org>
cc: "'Seth Russell'" <seth@robustai.net>, <www-rdf-interest@w3.org>
Message-ID: <Pine.LNX.4.30.0101231257360.17062-100000@tux.w3.org>

Hi Tod,

On Tue, 23 Jan 2001, Matola,Tod wrote:

>
> > -----Original Message-----
> > From: Seth Russell [mailto:seth@robustai.net]
> > Sent: Monday, January 22, 2001 9:32 AM
> > To: Libby Miller
> > Cc: McBride, Brian; www-rdf-interest@w3.org
> > Subject: Re: RDF IG meeting at W3C Technical Plenary 2001-02-28
> >
> >
> > Libby Miller wrote:
> >
> > > >  o Query - I'd be very interested to learn about ongoing
> > > >    work in RDF query.
> > >
> > > I totally agree - once querying RDF is implemented well, a
> > whole lot of
> > > things get much easier. It would be excellent to compare notes with
> > > people working in this area.
> >
> > Personally I don't believe we want a query language outside
> > of RDF .. we
> > want it inside RDF.   In other words we should be able to express a
> > question in RDF.  See my proposal [1] for implementing the who, where,
> > when, why, what pronouns.
> >
> > [1]
> > http://lists.w3.org/Archives/Public/www-rdf-interest/2001Jan/0142.html
> >
> > Seth
> >
> >
>
> I agree as well. I have been leaning towards something like:
> RDF Query Specification [1]
> from Ashok Malhotra (IBM) <petsa@us.ibm.com>  and Neel Sundaresan (IBM)
> <neel@almaden.ibm.com>
>
> Just wonder how others felt about it.
>
> Second what would the result of such a query (regardless of the QL) be? A
> list of triples, a list of lists of triples, a RDF document or list of RDF
> documents?


In http://www.w3.org/TandS/QL/QL98/pp/enabling.html we present a simple
query language where...

[[
The query is itself simply an RDF model (i.e., a directed labelled graph),
some of whose resources and properties may represent
variables. There are two outputs to every query,

    1.A subgraph (of the KB against which the query is issued) which
	matches the query.
    2.A table of sets of legal bindings for the variables, i.e., when
	these bindings are applied to the variables in the query, we get
       (1).
]]

In particular...:

[[
	One of the results of a query is itself an RDF knowledge base. This
	means that it is possible to issue a query against the
        result of another query. In this sense, this query language is
	similar to relational query languages. This feature will make it
        possible to construct recursive queries.
]]

So we've got a table-vs-rdfgraph duality thing going on when representing
the resultset from such a query. Sometimes you'll want to treat the
returned data just as a bunch of RDF, ie. those triples implicated in the
various possible answers to the query. And sometimes you'll prefer to
treat it as a tabular result-set a la JDBC/ODBC. In fact its possible
(though not necessarily wise -- discuss!) to overload the Java JDBC
machinery to talk to this kind of RDF query system. Libby's done something
in this vein building on top of Brian's Jena API, and we've had some brief
lunch discussions about augmenting a Jena-like API to provide innate
support for this sort of query interface. And there are doubtless a bunch
of scenarios  where you'll want a more sophisticated query language than
'graphs with question marks'. But anything in this vein is much nicer for
application writers than grovelling around at the node-and-arc level...

Dan







> [1] http://www.w3.org/TandS/QL/QL98/pp/rdfquery.html
>
Received on Tuesday, 23 January 2001 13:26:30 GMT

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