From: Andy Seaborne <andy.seaborne@talis.com>

Date: Fri, 28 May 2010 10:54:54 +0100

Message-ID: <4BFF92EE.7060302@talis.com>

To: Steve Harris <steve.harris@garlik.com>

CC: SPARQL Working Group <public-rdf-dawg@w3.org>

Date: Fri, 28 May 2010 10:54:54 +0100

Message-ID: <4BFF92EE.7060302@talis.com>

To: Steve Harris <steve.harris@garlik.com>

CC: SPARQL Working Group <public-rdf-dawg@w3.org>

On 28/05/2010 8:10 AM, Steve Harris wrote: > Overall seems pretty sensible, but there's one proposal that I'm not > clear on: > > "PROPOSED: The cardinality of solutions to fixed-length paths > is the same as the cardinality of solutions to the path expanded into > triple patterns (with all variables projected); the cardinality of > solutions to variable-length paths is the cardinality of solutions > via paths that do not repeat nodes; the cardinality of solutions to > paths combining fixed and variable length (elt{n,} ) is a combination > of the fixed definition plus the variable definition for paths longer > than the fixed length." > > I've read the minutes, but it's a little hard to interpret this proposal > without known-good examples. > > I'm guessing this means that ?x :p/:q* ?y is variable length path and so > that part of the solution is effectively distinct? Another > interpretation is that the :p sub-path is fixed length, so only the :q > part of the path is distinct. > > - Steve Steve - this particular proposal is more of an outline of how to attack the problem, rather than a choice between alternative designs. "?x :p/:q* ?y" a path combining fixed and variable length parts. The cardinality should reflect that (e.g. not be less that ?x :p ?y because that's a subcase :p/:q*). Where it says "plus", I think that "plus" is English "and also" - in technical terms, it's multiply: all the possiblities of the first part multipled by all the possiblities of the second part and :q* is distinct so it's multiple by one, but this is detail to be explored. The principle reflected in the proposal, is that {?x :p/:q* ?y} === {?x :p ?z . ?z :q* ?y} with ?z projected away. Now we have a design principle, I'm hopeful that we can answers these sorts of questions from that point of view. What we need is (lots of) test cases. (Hint, hint :-) AndyReceived on Friday, 28 May 2010 09:55:19 UTC

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