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Re: allow implicitly unbound variables in SPARQL results?

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Tue, 04 Oct 2005 12:33:35 +0100
Message-ID: <4342688F.7050305@hp.com>
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>

Steve Harris wrote:
> On Mon, Oct 03, 2005 at 05:18:52 -0500, Dan Connolly wrote:
>>Reviewing last call comment status, this one is (a) not connected
>>to an open issue, (b) not just editorial, and (c) hasn't
>>gotten much airtime.
>>This request seems pretty reasonable:
>>There are at least two ways to trim the results back down with just
>>syntax changes.  The least intrusive change would be to just drop the
>><unbound> tag, and have it be implicit with <binding name=".."/>.  More
>>drastic is to just drop the entire <binding> tag when the variable is
>>unbound, since the information can be retrieved from the head.
>> -- SPARQL Results Format and Unbound Variables
>>http://www.w3.org/mid/42F4CEEB.5090306@umd.edu aka
>>So how about we make <binding> elements for unbound variables
> Optional meaning may or may not be there I'm oposed to, but optional
> (w.r.t. the schema) meaning they must not be there if the variable is
> unbound would get my vote, though I believe it makes writing XSLT sheets
> harder.
> - Steve

Having it there sometimes is the most invconvenient.

As to whether to put it in always or never, I'm neutral.

- - - - - - - -

If the UNION has disjoint variable sets, then using OPTIONALs works and does 
not require a new operator in the algebra.



PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
  ?person a foaf:Person.
  { ?person foaf:name ?name } UNION
  { ?person foaf:mbox ?mbox } UNION
  { ?person foaf:homepage ?homepage } UNION
  { ?person foaf:mbox_sha1sum ?mbox_sha1sum } UNION
  { ?person foaf:nick ?nick } UNION
  { ?person rdfs:seeAlso ?seeAlso }

is more compactly done with OPTIONALs.

Multi-arity predicates seem to be OPTIONALS with more than one triple pattern 
if I understand proposed usage correctly.

Received on Tuesday, 4 October 2005 11:34:25 UTC

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