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

Date: Fri, 28 May 2010 12:12:57 +0100

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

Message-Id: <747873DD-18EA-4E3E-BFC7-15202AB28B87@garlik.com>

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

Date: Fri, 28 May 2010 12:12:57 +0100

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

Message-Id: <747873DD-18EA-4E3E-BFC7-15202AB28B87@garlik.com>

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

On 2010-05-28, at 10:54, Andy Seaborne wrote: > 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} Cool, thanks, that answers the question. - SteveReceived on Friday, 28 May 2010 11:13:35 UTC

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