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Re: evaluating SPARQL w.r.t an RDF query language survey

From: Dan Connolly <connolly@w3.org>
Date: Wed, 06 Apr 2005 17:21:56 -0500
To: Jos De Roo <jos.deroo@agfa.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-Id: <1112826117.15073.778.camel@localhost>

On Wed, 2005-04-06 at 22:13 +0200, jos.deroo@agfa.com wrote:
> picking out just one case.. (have tested 11 cases a while back)
> 
> > 10 Namespace
> > Return all resources whose namespace starts with
> > "http://aifb.uni-karlsruhe.de/".
> >
> > seems to have a typo in the question...
> > missing www.
> >
> > select ?R where
> >  { ?R ?x ?y.
> >    FILTER regex(str(?R), "http://www.aifb.uni-karlsruhe.de/")
> > }
> 
> why not simply
> 
> SELECT ?R
> WHERE {?R a rdfs:Class;
>           log:uri ?S.
>        ?S str:matches "http://www\.aifb\.uni-karlsruhe\.de/.*"}

That basically involves changing the way DataSets and background
graphs work so that they always include "axiomatic" triples
such as
  <http://www.aifb.uni-karlsruhe.de/> log:uri
"http://www.aifb.uni-karlsruhe.de/".
and
  "a" str:matches "a".

That was not a popular design when it was discussed in Helsinki
under issue useMentionOp
  http://www.w3.org/2001/sw/DataAccess/ftf4.html#itemumop
 <- http://www.w3.org/2001/sw/DataAccess/issues#useMentionOp

Let's see... no, you weren't there for that one. You might
want to look over the record of that item and see if the
rationale/discussion there satisfies you. (I think I meant
to abstain but was too busy chairing to get my abstention
recorded.)

If not, you can ask to re-open the issue.

> or some such (I don't have enough regex experience)
> 
> 
> I'm even more convinced after reading
> http://www.w3.org/2005/03/position2.html
> 
> [[
> Built-in Functions and operators: Use RDF Properties
> 
> ... All this speaks against built-in functions being
> brought out as special syntax, and supports the use of
> RDF properties for them.
> ]]

That's new information since the Helsinki meeting, I suppose.

Another thing that's sorta new information is that triple
patterns can have literal subjects.

I'm not yet convinced the issue should be re-opened, but
everything is negotiable.

> The point is also about that separate FILTER, I'm not
> convinced at all and basically a query is already a
> filter rule
> 
> {where-triple-pattern} => {construct-or-select-triple-pattern}
> 
> I just don't see the benefit of having FILTER in filter..

FILTER expressions behave much more like traditional programming
language expressions. While there are some "unknown" cases in
the corners, most expressions are closed over negation, unlike
triple patterns.

Oops... I slipped into arguing... I really shouldn't do much
of that for issues that are closed.

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Wednesday, 6 April 2005 22:21:58 GMT

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