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Re: On told-bnodes in queries

From: Enrico Franconi <franconi@inf.unibz.it>
Date: Sat, 5 Nov 2005 17:47:23 +0100
Message-Id: <22756018-6FC4-4B69-902A-D6CA4CA9DA26@inf.unibz.it>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: Pat Hayes <phayes@ihmc.us>

Pat,
you have to have a mechanism that distinguishes the use of a bnode as  
a normal bnode from a told-bnode. Otherwise, in the case you don't  
want to use told-bnodes, how can you avoid possible clashes between  
the (arbitrary) bnode names chosen for the query, and the (unknown)  
bnodes in the graph? That's why you need merge-union. And that's why  
you then need a mechanism to make a distinction between the two  
different meanings of a bnode in the query.
All your cases are covered by our simple semantics; but we guarantee  
safety in the case the user does not know the bnode names in the  
original graph while you don't have such a guarantee. If you think  
about it, the way to fix your weak semantics is to have a union  
semantics *after* you have renamed the bnodes that you don't want to  
use as told-bnodes. Well, this is what we do: we first have to  
provide a syntax to distinguish which role should a bnode play in the  
query, and then we make sure that for the bnodes to be treated as  
told-bnodes in the query the coreference with the dataset bnodes is  
possible. That's our semantics.
--e.
Received on Saturday, 5 November 2005 16:47:44 GMT

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