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Re: "the graphs referred to in the FROM clauses" [comment: major technical: underspecified errors] (SOURCE, rdfSemantics)

From: Dan Connolly <connolly@w3.org>
Date: Fri, 13 Jan 2006 12:27:09 -0600
To: Pat Hayes <phayes@ihmc.us>
Cc: public-rdf-dawg@w3.org
Message-Id: <1137176829.4991.57.camel@dirk.w3.org>

On Fri, 2006-01-13 at 12:01 -0600, Pat Hayes wrote:
> >In "major technical: underspecified errors"
> >http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2006Jan/0066.html
[...]
> Why do we want to keep the names attached to the FROM NAMED graphs? 
> Can a query variable bind to the name of a graph in the dataset?

Yes.

That's one of the main uses of the GRAPH keyword; here's an
example from the spec:

[[
SELECT ?mbox ?nick ?ppd
WHERE
{
  GRAPH data:aliceFoaf
  {
    ?alice foaf:mbox <mailto:alice@work.example> ;
           foaf:knows ?whom .
    ?whom  foaf:mbox ?mbox ;
           rdfs:seeAlso ?ppd .
    ?ppd  a foaf:PersonalProfileDocument .
  } .
  GRAPH ?ppd
  {
      ?w foaf:mbox ?mbox ;
         foaf:nick ?nick 
  }
]]
 -- http://www.w3.org/2001/sw/DataAccess/rq23/#restrictInQuery

The GRAPH keyword is our solution to the SOURCE issue, on which
the WG spent considerable time, and closed despite outstanding
objections regarding requirements.

  http://www.w3.org/2001/sw/DataAccess/issues#SOURCE



>  If 
> so, we need to re-write the basic definitions to allow for this.

We have discussed a sort of wink-nudge approach to the semantics
of GRAPH. We talked about a sort of health-warning, a la

  We're not exactly sure what the formal semantics of GRAPH are.
  Use with care.

(I'm not sure which teleconference this was in, nor whether it
was recorded at the time; no matter; the issue is still open.)

I am unable to resist reminding everybody that I advised us
not to go here:

"DanC argued against taking us out of the scope of positive conjunctive
queries against RDF graphs."
 -- http://www.w3.org/2001/sw/DataAccess/ftf4.html

and the issues lists also notes a comment on this from Klyne:

"I also feel it would be premature to standardize an approach to
multi-graph querying ahead of there being a consensus/standard for
something like RDF named graphs."
 --
http://lists.w3.org/Archives/Public/public-rdf-dawg-comments/2005Apr/0010.html


> Pat

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Friday, 13 January 2006 18:27:24 GMT

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