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Re: rq23 def'n "Pattern Solution" wrong? (and more on BGP')

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Wed, 1 Mar 2006 18:09:55 +0100
Message-ID: <1141232995.4405d563176ac@www.inf.unibz.it>
To: Lee Feigenbaum <feigenbl@us.ibm.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

Quoting Lee Feigenbaum <feigenbl@us.ibm.com>:
> Enrico Franconi wrote on 02/28/2006 07:45:00 PM:
> > On 1 Mar 2006, at 00:02, Pat Hayes wrote:
> > >> - if we don't have BGP', the (abstract syntax representation of
> > >> the) answer set can not use bnodes which appear in the (abstract
> > >> syntax representation of the) query;
> > >
> > > That is true
> > 
> > That's enough for me.
> Perhaps for you it is :-), but as someone who is striving to put a
> good 
> faith effort to fully understand this debate to both make informed 
> decisions in the future and to be able to educate SPARQL users and 
> implementors within my organization, I'd like to ask you, Enrico, to
> address the full response that Pat made rather than to take these
> three words out of context. 

I don't think there is anything to add to what I said in my original
mail, but I will repeat it again.

> In particular, if I understand Pat correctly (please correct me if I
> do 
> not), then he is stating that BGP' enables an ability that has never
> been 
> discussed by the DAWG (presumably that does not have approved use
> cases or 
> requirements driving it?) and also an ability for which no work has
> been 
> done to fully enable due to other factors. Specifically, Pat observes
> that 
> the SPARQL result document explicitly scopes bnode IDs to that
> document, 
> and so there is no current mechanism by which an answer document
> could (in 
> the concrete syntax) refer to bnodes mentioned in the query. (Pat
> writes: 
> "it would involve having partially overlapping bnode scopes between
> the 
> query and answer documents")
> Could you please spare a few sentences (or a pointer to an earlier
> message 
> if you feel this has already been addressed) that addresses these two
> points?


1) In the first part of my original message I argued that, by carefully
looking at the normative semantics RDF-MT, bnodes are always
interpreted autonomously within the RDF graph where they appear, no
matter where bnodes come from or which (abstract) syntax identity they
have. So, while this is an argument againts having BGP', this also
shows that it is absolutely harmless to have BGP'.

2) In the second part of my original message I argued that if we don't
have BGP' then the abstract syntax of answer sets is limited in a very
peculiar way, disallowing answer sets that contains bnodes that may
appear in the query. This restriction is useless, since we know (point
1 above) that bnodes are always interpreted autonomously within the
graph where they appear, so having the same bnodes as in the query is
fine anyway. This restriction is bad, since not every equivalent answer
set would be legal in sparql.

Received on Wednesday, 1 March 2006 17:10:11 UTC

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