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Re: Objections to current SPARQL specification

From: Andrew Newman <andrewfnewman@gmail.com>
Date: Fri, 2 Nov 2007 13:01:22 +1000
Message-ID: <2db5a5c40711012001l93c61a1g3a74981b6d735f90@mail.gmail.com>
To: "Eric Prud'hommeaux" <eric@w3.org>
Cc: public-rdf-dawg-comments@w3.org

This is close but not quite right.

I'd say, "Such a language would not only produce sets of variables but
also allow the production of RDF graphs".

I also fully agree with the extraction of terms from an RDF graph in
Requirement 3.2.  The stage at which the extraction from an RDF graph
should take place at projection not at the graph matching stage.

I'd also suggest that the implementation of SPARQL in JRDF
(http://jrdf.sf.net/) is a conceivable alternative form of the
language that does meet these goals.

> [[
> In objection 8, Andrew Newman objects to the early direction of
> SPARQL, preferring an RDF query language based on manipulations of
> graphs. Such a language would not produce sets of variables, but
> instead produce only RDF graphs.
>
> The first document published by the Working Group was the RDF Data
> Access Use Cases and Requirements [UCR]. Requirement 3.2, Variable
> Binding Results [VBR] requires the extraction of terms from the RDF
> graph into a set of solution tuples. No yet-concieved form of a
> language meeting the commentor's design goals meets this requirement.
>
> [UCR] http://www.w3.org/TR/2005/WD-rdf-dawg-uc-20050325/
> [VBR] http://www.w3.org/TR/2005/WD-rdf-dawg-uc-20050325/#r3.2
> ]]
>
> > The basis of my objection is founded on SPARQL being an RDF query
> > language and that it should use an RDF data model throughout.  This is
> > one property that represents what is considered good design for query
> > languages (for RDF query languages see [1] but it has been covered
> > elsewhere in criticism of other query languages such as SQL).
> >
> > One feature that SPARQL lacks is closure.  Having closure on all
> > operations means that intermediate results and answers are always tied
> > to an RDF graph.  It means that in each step of the query evaluation
> > you are dealing with valid subsets of RDF graphs.  The current
> > specification, however, reverts to an SQL/multiset/bindings to
> > variables that is not compatible with the RDF model.
> >
> > To summarize, my objections include [2][3][4][5]:
> > * Lack of closure.
> > * Inconsistencies between SPARQL triples and the currently defined RDF
> > standard (requiring special handling of say CONSTRUCT when there are
> > literals as subjects).  If SPARQL was defined in terms of RDF, if RDF
> > changed then SPARQL would naturally change.  The current way the
> > specification was created seems to allow a difference between the
> > language and the data it's querying.
> > * The use of multiset semantics instead of semantics consistent with
> > RDF (set based semantics).
> > * The multiple uses of unbound - you cannot distinguish between a
> > result from an OPTIONAL operation or from a variable that is not used
> > in the query.  This prevents it from being understood, without
> > retaining the original query, what unbound means.
> > * Existence of DISTINCT and REDUCED (set based semantics don't have duplicates).
> > * Existence of CONSTRUCT (should just be a projection of all columns).
> > * Existence of ASK (should just be a projection of no columns giving
> > DEE or DUM, T/F).
> > * Lack of nadic operators (JOIN, UNION and possibly OPTIONAL).
> > * Lack of SUMMARIZE (set based aggregate function).
> >
> > [1] J. Bailey et al, "Web and Semantic Web Query Languages: A Survey,"
> > LNCS 3564, 2005, Norbert Eisinger, Jan Maluszynski (editor(s)),
> > [2] http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2006Nov/0006.html
> > [3] http://jrdf.sourceforge.net/thesis/2006/RelationalBasedSPARQL.html
> > [4] http://www.xml.com/lpt/a/1695
> > [5] http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2004Nov/0001.html
>
> --
> -eric
>
> office: +1.617.258.5741 NE43-344, MIT, Cambridge, MA 02144 USA
> mobile: +1.617.599.3509
>
> (eric@w3.org)
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Received on Friday, 2 November 2007 03:01:32 GMT

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