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Re: entailment review - part 2

From: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
Date: Tue, 12 Jan 2010 12:58:25 +0000
Message-ID: <492f2b0b1001120458s2d306eb9p36ff98fb6fec4838@mail.gmail.com>
To: Axel Polleres <axel.polleres@deri.org>
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
Axel,
we've spend some more thoughts on the inconsistency issue here.

>>> > I am not sure, actually, condition 1. doesn't require consistency of SG, it only says:
>>> > "The scoping graph, SG, corresponding to any consistent active graph AG is uniquely specified and is E-equivalent to AG."
>>> >
>>> > So, hmmmm, *actually*, this wording actually doesn't limit at all what the scoping graph to an
>>> > inconsistent graph is: In fact, this even seems to let open that the SG for an inconsistent
>>> > graph is e.g. empty, implementation dependent, etc.

I now discussed that with Boris (Ian is super busy at the moment) and
in our understanding the SG is at best undefined if AG is inconsistent
or, rather, there is no scoping graph in that case. Thus, if AG is
inconsistent, then you could do something that does not use a scoping
graph, but if you do that, you violate condition 3 that basically says
that SG must entail the answers. Condition 3 cannot be satisfied if
you have no SG or SG is undefined and you cannot have an SG because SG
would have to be consistent (E-equivalence).

Birte
Received on Tuesday, 12 January 2010 12:58:57 GMT

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