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Re: SPARQL syntax proposals

From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
Date: Sat, 5 Mar 2005 16:48:39 +0000
To: public-rdf-dawg@w3.org
Message-ID: <20050305164839.GB16967@login.ecs.soton.ac.uk>

On Sat, Mar 05, 2005 at 03:31:14 +0000, Andy Seaborne wrote:
> 
> 
> Steve Harris wrote:
> >On Fri, Mar 04, 2005 at 02:52:17 +0000, Dave Beckett wrote:
> >
> >>On Thu, 2005-03-03 at 16:51 -0500, Eric Prud'hommeaux wrote:
> >>
> >>
> >>>as promised, AND is now FILTER:
> >>>SELECT ?who
> >>>WHERE { ?who :age ?n. FILTER ?n + 1 < 5 }
> >>
> >>This I like, as it was pretty much how I thought about constraints - get
> >>a bunch of triples then filter them with a big expression.
> >
> >
> >Its cleaner than AND, but I think we should avoid
> >
> >FILTER ?x + 1 < 4 FILER ?y + 2 < 4
> 
> Allowing FILTER to be close to a triple that binds the variable it tests is 
> natural:
> 
> {
>    <v> :p ?x . FILTER ?x < 4 .
>    <v> :q ?y . REGEXP(?y, "foo", "i") .
> }

I personally find that quite hard to read, and should that be FILTER
REGEXP ...
 
> Nothing to do with which syntax here.
> 
> So I think that would need at least one dot to separate adjacent FILTERs 
> without making special cases to drop the separator for FILTER and/or to 
> keep them apart.
> 
> {
>   <v> :p ?x ;
>       :q ?y .
> 
>   FILTER ?x + 1 < 4 .
>   REGEXP(?y, "foo", "i") .
> }
> 
> seems OK.  A corner case is:
> 
>   FILTER ?x + 1 < 4  <http://> :p ?v .

Also, FILTER ?x < 4.

which could be the floating point number 4.0, or the integer 4 and a
terminator. (I didn't check if we do 4. or .4, but many languages do,
including SQL).
 
> i.e. a triple pattern after a FILTER - not a problem technically unless (*) 
> literals-as-subject appear and we have unary +/-
> 
>   FILTER ?x + 1 < 4  -2 :p ?v .
> 
> which is icky (enough lookahead (3?) resolves but the error messages are 
> likely to be quite confusing).

Its all icky. I think one of the things we should take away from SQL is
that clearly dividing up the logical regions of the query makes it easier
to read other peoples queries.

- Steve
Received on Saturday, 5 March 2005 16:53:45 GMT

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