- From: Enrico Franconi <franconi@inf.unibz.it>
- Date: Thu, 26 Jan 2006 12:35:40 +0100
- To: Andy Seaborne <andy.seaborne@hp.com>
- Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
On 26 Jan 2006, at 12:22, Enrico Franconi wrote: > Since now you changed the text to have G no more equal to G', the > following does not hold anymore: > > """ > A pattern solution can then be defined as follows: to match a basic > graph pattern under simple entailment, it is possible to proceed by > finding a mapping from blank nodes and variables in the basic graph > pattern to terms in the graph being matched; a pattern solution is > then a mapping restricted to just the variables. Moreover, the > uniqueness property of pattern solutions guarantees the > interoperability between SPARQL systems: given a graph and a basic > graph pattern, the set of all the pattern solutions is unique. > """ > > So, if you want to keep the change, in both cases you have to add > "modulo arbitrary renamings of the bnodes". > > Still, I argue that the change shouldn't have been made. What puzzles me, in addition to what I did say in <http:// lists.w3.org/Archives/Public/public-rdf-dawg/2006JanMar/0282>, is that also the following statement becomes false: """ When using simple entailment, the operation of querying an RDF graph provides access to the graph structure; nothing that is not already in the graph G needs to be inferred or constructed, even implicitly. """ This is false since now we allow for some semantics to sneak in: it says that graphs are (logically) equivalent if they have different bnode names. If I understand the main motivations of this first version of SPARQL, this should not happen. We have just syntax in this version of SPARQL. So, we should really have G=G' in the definition of SPARQL Basic Graph Pattern Matching. comments? --e.
Received on Thursday, 26 January 2006 11:35:46 UTC