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Re: More on MINUS vs. UNSAID

From: Lee Feigenbaum <lee@thefigtrees.net>
Date: Mon, 27 Jul 2009 17:41:06 -0400
Message-ID: <4A6E1EF2.3020000@thefigtrees.net>
To: Eric Prud'hommeaux <eric@w3.org>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>, "Seaborne, Andy" <andy.seaborne@hp.com>
Eric Prud'hommeaux wrote:
> ISSUE-29
> I believe this definition of Minus in SPARQL algebra is practical for all use cases:
>   Definition: Minus
>   Let Ω1 and Ω2 be multisets of solution mappings. We define:
>   Diff(Ω1, Ω2, expr) = { μ | μ in Ω1 such that for all μ′ in Ω2, μ and μ′ are not compatible }
>   card[Diff(Ω1, Ω2, expr)](μ) = card[Ω1](μ)
> which is the same as Diff (Ω1, Ω2, true)
>   http://www.w3.org/TR/rdf-sparql-query/#defn_algDiff

That's the same as the MINUS-AntiJoin from my message 

I don't think that matched the intuition of most people that advocated 
MINUS on the teleconference, who preferred this definition with the 
added restriction that prevented removing solutions from the left-hand 
side that share no variables in common with any solutions from the 
right-hand side. (MINUS-AntiJoin+Restriction)

Received on Monday, 27 July 2009 21:42:03 UTC

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