[Mulgara-general] Removing exclude.

[Andrae Muys]

My current focus is on the Non-union compatible disjunction bug.  As  
a part of this I am back in TuplesOperations.project() and friends,  
where there is some ugliness resulting from the current  
implementation of exclude.  I'm not going to get sidetracked on a  
cleanup job, but it does remind me that we never did reach an  
agreement on the future of exclude.

As I recall the conversation we hadn't yet found anyone who actually  
uses it - and of those who have tried to, no-one has managed to  
actually use it correctly.  It was introduced to provide a limited  
form of negation, and one that interacts poorly with the open-world  
assumption.  We also now have minus, which is well defined,  
corresponds closely to our intuitive understanding of the operation,  
and is (I am told) what was actually required.

If my memory is correct we should probably at least deprecate, if not  
remove exclude entirely from mulgara.

Do we agree that exclude should be removed?

If it should be removed, when should this occur?

Andrae

-- 
Andrae Muys
andrae at netymon.com
Principal Mulgara Consultant
Netymon Pty Ltd