- From: Lee Feigenbaum <feigenbl@us.ibm.com>
- Date: Tue, 14 Feb 2006 01:53:05 -0500
- To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Hi everyone, Forgive me if this has been discussed already and I'm missing something. The definition of Pattern Solution currently in 2.4 says: """ A pattern solution, S, is a variable substitution whose domain includes all the variables in V and whose range is a subset of the set of RDF terms occurring in G. """ I believe that the range of S is really a subset of the terms appearing in the scoping graph, G', correct? Unfortunately, the scoping graph has not been defined at this point in the document. Perhaps the definition should be rewritten to be parametrized on the identity of G? Currently, the definition is followed immediately by: """ A pattern is matched against the target graph. """ This seems to indicate that G is the target graph for the above definition, whereas we actually want G in the Pattern Solution definition to be the scoping graph. thanks, Lee PS -- I ran across this while finally having a chance today to spend several hours going over the discussion between Enrico, Sergio, Jos, and Pat about the issues surrounding BGP' in the rq23 E-matching definitions. To the best that I can tell, the use of BGP' in these definitions does not break anything at all; Pat seems to argue that the presence of BGP' breaks CONSTRUCT queries because it allows answer bindings to be introduced with bnodes that clash between BGP and G'. Pat says a few times that this might create a problem when substituting Si(BGP) to create the CONSTRUCT output graph, but as Sergio pointed out, the CONSTRUCT output graph is made up of substitutions into the Ti template pieces, which are not related to BGP. In fact, once BGP has morphed into BGP', answers are never again substituted into BGP, which is one reason that I feel that the current definitions are correct. Pat, I'd appreciate it if you could explain to me (online or offline), if you think that there is still a technical deficiency in the current definitions... A full example would be most helpful, as the example in the existing threads is fragmented and incomplete. That being said, it is only since the January 26th decision that Pat has elucidated the correctness justifications for the simpler definitions (w/o BGP' or OrderedMerge, simply requiring that G E-entail (G' union S(BGP))). I find Pat's arguments concerning the distinction between the mathematical bnode objects (which have no scope but global) and bnode IDs (which we must carefully scope between documents) to be convincing, and I have not found an example or general justification from Enrico or Sergio (or Jos) that in particular addresses Pat's recent claims that the simpler definitions work (and that claims to the contrary are due to a conflation of bnodes and bnode IDs). All this is to say that while I am OK with the current definitions because I do not believe them to be broken, I would prefer the simpler definitions in lieu of evidence that the simpler definitions do not work correctly. Enrico, Sergio, Jos, or anyone else, as with Pat above, I'd appreciate if you could explain to me (online or offline) why you feel that the simpler definitions (the so-called "Pat H definitions") require the addition of the BGP' construct. Many thanks!
Received on Tuesday, 14 February 2006 06:53:15 UTC