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Re: summary on options for JP-4 Comment about the semantics of property paths

From: Gregory Williams <greg@evilfunhouse.com>
Date: Thu, 9 Feb 2012 16:25:10 -0500
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
Message-Id: <56655160-B537-4429-9AFF-CE5A70E48EA7@evilfunhouse.com>
To: Axel Polleres <axel.polleres@deri.org>
On Feb 9, 2012, at 4:10 PM, Axel Polleres wrote:

> Option 2 ... add DISTINCT around paths: It seems that sticking to our intended semantics and allowing - orthogonally to their
> ALLPATHS keyword proposal the keyword DISTINCT( ) around path expressions switching to existential paths semantics would be
> equivalent to the JP-4 existential paths semantics as outlined in Section 7.1 of their paper, and thus optimizable.

I don't like the idea of adding a second set of property path semantics this late in the game. Beyond not wanting two semantics, I think it would be very premature to change the syntax by just slapping DISTINCT() around a property path. I'm worried that it would unnecessarily complicate the grammar (it seems possible that distinct subqueries might already capture what's being asked for) and could conflict with future grammar extensions (e.g. to support things like property path lengths, something which we specifically discussed and wanted to leave open for future work/standardization).

.greg
Received on Thursday, 9 February 2012 21:25:35 GMT

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