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NOT EXISTS vs. MINUS

From: Jeen Broekstra <jeen.broekstra@gmail.com>
Date: Thu, 20 Jan 2011 17:32:57 +1300
Message-ID: <4D37BAF9.7020001@gmail.com>
To: public-rdf-dawg-comments@w3.org
Hello,

I am seeking clarification on the part of the spec about negation, 
specifically the difference between NOT EXISTS and MINUS.

If my understanding of section 8.3 is correct, the only cases in which 
NOT EXISTS and MINUS produce different results is in those cases where 
the pattern on the right-hand side has no shared variables with the 
left-hand side, correct?

However, as far as I can tell, a MINUS having no shared variables with 
the lhs graph pattern by definition has no influence on the query result.

If that is so, I'm probably missing what the exact point is of MINUS. In 
what practical situation is it envisioned to be significantly different 
from just using NOT EXISTS?


Regards,

Jeen Broekstra
Received on Thursday, 20 January 2011 08:41:02 GMT

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