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RE: Requirement 3.6: Optional Match

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Fri, 7 May 2004 14:01:18 +0100
Message-ID: <E864E95CB35C1C46B72FEA0626A2E808031A907C@0-mail-br1.hpl.hp.com>
To: Rob Shearer <Rob.Shearer@networkinference.com>, RDF Data Access Working Group <public-rdf-dawg@w3.org>



-------- Original Message --------
> From: Rob Shearer <mailto:Rob.Shearer@networkinference.com>
> Date: 6 May 2004 20:39
> 
> I'm afraid I can't really support this as a requirement, although I
> think features which allow this result (albeit not necessary directly)
> would almost certainly be extremely useful.
> 
> The thing is, "optional bindings" are really nothing more than unions
> between independent queries: union the results of the query with the
> binding with the results of the query without it. I'd say a more
> general-purpose "union" operator is quite a bit more
> important than this
> one particular form, and even then I'm not sure whether it
> rises to the
> level of requirement.

Expressing it as "Optional Matching" makes it more user-centric.  It covers
features that are being requested by users (application writers).

Getting AB? (where A and B are graph patterns, ? is  0 or 1) as union(A, AB)
might be OK but as the choices grow we get:

	AB?C? = union(A, AB, AC, ABC)

	Andy


> 
> > -----Original Message-----
> > From: public-rdf-dawg-request@w3.org
> > [mailto:public-rdf-dawg-request@w3.org] On Behalf Of Seaborne, Andy
> > Sent: 06 May 2004 08:40 To: RDF Data Access Working Group
> > Subject: Requirement 3.6: Optional Match
> > 
> > 
> > 
> > I suggest what I think are small changes:
> > 
> > + including the term "graph pattern" as is in the suggested
> > text for 3.1.
> > + tweaking the title
> > + Be neutral to "optional triples" and "may-bind" variables.
> > 
> > ------------------------
> > 
> > 3.6 Optional Matching
> > 
> > It must be possible to express a query graph pattern that
> > does not fail to
> > match when some nominated part of the graph pattern fails to
> > match.  Any
> > such triples matched by this optional part, or variable
> > bindings caused by
> > this optional part, can be requested in the results.
> > 
> > ------------------------
> > 
> > 	Andy
> > 
> > 
> > 
> > 
> > For reference, the text in v1.39 is:
> > """
> > 3.6 Optional Match
> > It must be possible to express a query that does not fail when some
> > nominated part of the query specifying "optional triples"
> > fails to match.
> > Any such triples matched by this optional part, or variable bindings
> > caused by this optional part, can be returned in the results, if
> > requested. """ 
Received on Friday, 7 May 2004 09:01:48 GMT

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