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RE: Testcase comment and question

From: Geoff Chappell <geoff@sover.net>
Date: Tue, 29 Mar 2005 17:33:57 -0500
To: "'Dan Connolly'" <connolly@w3.org>
Cc: <public-rdf-dawg-comments@w3.org>
Message-ID: <015601c534af$659d83b0$6401a8c0@gsclaptop>



> -----Original Message-----
> From: Dan Connolly [mailto:connolly@w3.org]
> Sent: Tuesday, March 29, 2005 4:58 PM
> To: Geoff Chappell
> Cc: public-rdf-dawg-comments@w3.org
> Subject: RE: Testcase comment and question
> 
> On Tue, 2005-03-29 at 14:50 -0500, Geoff Chappell wrote:
> >
> > > -----Original Message-----
> > > From: Dan Connolly [mailto:connolly@w3.org]
> > > Sent: Tuesday, March 29, 2005 12:02 PM
> > > To: public-rdf-dawg-comments@w3.org; Geoff Chappell
> > > Subject: Re: Testcase comment and question
> > >
> >
> > > Both the current editor's draft and the latest public working
> > > draft give this formal specification:
> > >
> > > [[
> > > Definition: Optional Matching
> > >
> > > Given graph pattern GP1, and graph pattern GP2, let GP = (GP1 union
> > > GP2).
> > >
> > > The optional match of GP2 of graph G, given GP1, defines a pattern
> > > solution PS such that:
> > >
> > > If GP matches G, then the solutions of GP is the patterns solutions of
> > > GP else the solutions are the pattern solutions of GP1 matching G.
> > > ]]
> >
> > Thanks. I guess it wasn't fair to imply there was no definition. I do
> think,
> > though, that this one will need some tightening up. For example it seems
> to
> > imply that if _any_ solutions can be found in GP, then no solutions will
> be
> > used from GP1.
> 
> Yes, that's what it says.
> 
> >  And assuming that's not the case,
> 
> Er... why not? Am I missing something?

One of us is, I guess :-)

Consider this graph:

@prefix foaf:  <http://xmlns.com/foaf/0.1/> .

_:a  foaf:name   "Johnny Lee Outlaw" .
_:a  foaf:mbox   <mailto:jlow@example.com> .
_:b  foaf:name   "Peter Goodguy" .

and this query:


PREFIX  foaf: <http://xmlns.com/foaf/0.1/>
SELECT  ?name ?mbox
WHERE
    { ?x foaf:name ?name .
      OPTIONAL ?x foaf:mbox ?mbox .
    }

Then according to the definition:

GP1 = {?x foaf:name ?name .}
GP2 = {?x foaf:mbox ?mbox .}
GP  = {?x foaf:name ?name . ?x foaf:mbox ?mbox .}

R(GP, G) = {<"Johnny Lee Outlaw", <mailto:jlow@example.com> >}
R(GP1, G)= {<"Johnny Lee Outlaw">, <"Peter Goodguy"> }

So by the definition, the answer to query is:

	{<"Johnny Lee Outlaw", <mailto:jlow@example.com> >}

since GP has solutions we use those. 

But surely we expect the results of the query to be:

	{<"Johnny Lee Outlaw", <mailto:jlow@example.com> >,
	 <"Peter Goodguy", unbound> }

i.e. a combination of the solutions - some from GP, some from GP1.

Geoff
Received on Tuesday, 29 March 2005 22:34:15 GMT

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