That seems like an excellent solution.
On Jul 2, 2010, at 6:35 AM, Henrique Lopes Cardoso wrote:
Hi,
I was trying to figure out a way of checking the "status" of some
system.
To make things simpler, I have two kinds of facts, start and end,
which
are added along time:
(deftemplate start)
(deftemplate end)
Then I want to say that I have an "active" system if it has started
and
not ended yet. However, I want to avoid doing like
(start) (not (end))
in every rule where I need to check if the system is active.
My first approach was to try backward chaining. In Prolog I would do
something like:
active :- start, not(end).
However in Jess this gets more complicated, since doing something
like:
(deftemplate active
(declare (backchain-reactive TRUE)) )
(defrule do-active
(need-active)
(start)
(not (end))
=>
(assert (active)) )
will assert the active fact, but then I need another rule to retract
active when end occurs...
I then turned to using the logical conditional element, which seems to
work fine:
(defrule active-ctx
(logical (not (end)))
(start)
=>
(assert (active)) )
Is this the best way of doing it?
Thanks.
Henrique
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Ernest Friedman-Hill
Informatics & Decision Sciences, Sandia National Laboratories
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