ISSUE-29: MINUS / NOT EXISTS

On 03/02/2010 1:42 PM, Lee Feigenbaum wrote:
>
>> ISSUE-29
>> Should negation be done via a binary operator on subqueries, a binary
>> operator within graph patterns, or a filter+subquery?      ??
>>   This is MINUS / NOT EXISTS issue.
>
> This might be a good place to start with a test case or three. Andy, do
> you happen to have any cases that illustrate the difference here?
>
> (I know that personally, my preference here is pretty much "no
> preference".)

You gathered:
http://lists.w3.org/Archives/Public/public-rdf-dawg/2009JulSep/0030.html


http://lists.w3.org/Archives/Public/public-rdf-dawg/2009JulSep/0137.html

shows that one can be used to implement the other in the majority of 
cases (it's the nested optionals case we had in SPARQL 1.0 in a 
different guise) but we don't have a definition of MINUS to accurately 
compare.  What's the cardinality in the results?

So it's not about implementation as I understand the problem space today.

I find it clearer to read and explain the EXISTS form - someone (Simon?) 
said he'd asked the same of an SQL expert and EXISTS is better 
understood by application writers than MINUS there.

The additional condition in MINUS ("dom(μ) and dom(μ') are disjoint") 
concerns me because I don't know what's being "MINUSed" - it's not a 
regular set/multiset operation and certainly not like SQL MINUS which is 
set difference.

 Andy

Received on Wednesday, 3 February 2010 14:53:26 UTC