Re: More on MINUS vs. UNSAID

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 
(http://lists.w3.org/Archives/Public/public-rdf-dawg/2009JulSep/0030.html), 
right?

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)

Lee

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