# Re: More on MINUS vs. UNSAID

From: Eric Prud'hommeaux <eric@w3.org>
Date: Tue, 28 Jul 2009 08:34:13 -0400
To: Lee Feigenbaum <lee@thefigtrees.net>
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>, "Seaborne, Andy" <andy.seaborne@hp.com>
Message-ID: <20090728123413.GA3192@w3.org>
```* Lee Feigenbaum <lee@thefigtrees.net> [2009-07-27 17:41-0400]
> 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?

yep

> 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)

yes again, let's fix that:

Diff(Ω1, Ω2, expr) = { μ | μ in Ω1 such that for all μ′ with non-empty dom() in Ω2, μ and μ′ are not compatible }
++++++++++++++++++++
> Lee
>
>

--
-eric

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