Hi Peter,
I miss these sorts of rules. I've used them for:
validating input objects i.e. if there is no <required thing> change the
output state to <error>
initial actions (without having to use state objects) i.e. if there is no
<grand total> assert a new NamedInteger("grand total", 0)
final actions (i.e. where you have been matching and retracting facts as
you go) - you can use conflict resolution strategies to achieve this too,
but I think using a not(X) condition is clearer and more portable
So far I've been able to do without, but I think the rules are less clear
sometimes as a result.
Adrian Bigland.
Peter Van Weert
<[EMAIL PROTECTED] To:
[email protected]
uleuven.be> cc:
Subject: [drools-user]
Necessity of negative conditions?
16/01/2006 15:55
Please respond to
user
Hi,
I was wondering what your opinions are on the necessity of negative
conditions in production rules? The reason I am interested is that I am
currently developing a Java embedding of a rule-based programming
language myself, with similar expressive power as the current Drools
language (i.e.: forward chaining rules without negative conditions). I
am pleased to see a system as Drools became this popular and widely used
and accepted without support for negative conditions. It strengthens my
feeling that a language could do without (and without the complexities
of implementing it efficiently...).
So, the main question for the discussion I am hoping to get started here
(probably you've had it before somewhere, in which case a summary of the
outcomes would be much appreciated): are negative conditions necessary?
Are they missed in practice a lot?
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