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Re: SPARQL syntax proposals

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Sat, 05 Mar 2005 15:31:14 +0000
Message-ID: <4229D0C2.3040402@hp.com>
To: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
Cc: public-rdf-dawg@w3.org



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") .
}

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 .

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).


	Andy

(*) rq23 does allow them in the definitions and references the note in RDF 
core.  The data wil not have any lierals-as-subjects if legal RDF so no 
matches.  We can control the syntax in SPARQL.

> 
> even though it makes sense if it has the same semantics as AND, it reads a
> bit oddly
> 
> I have a mild preference for a closer relationship to SQL:
> 
> SELECT ?var FROM { :a :b ?var } WHERE ?var < 3
> 
> But I can see why that might be confusing.
> 
> - Steve
> 
Received on Saturday, 5 March 2005 15:36:59 GMT

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