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Re: Property Paths Cardinality

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>
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.

- Steve
Received on Friday, 28 May 2010 11:13:35 GMT

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