-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of Wolfgang Laun
Sent: woensdag 20 februari 2008 15:41
To: [email protected]
Subject: Re: JESS: Rules for detecting changes of a multislot
Martijn Tromm wrote:
Lars,
With activations and retractions I was thinking about something like
this:
For every object in (c (m a b c)) assert a separate relation-fact
(object ?x) and keep a object-status template-fact for reference. Once
an object gets asserted it will be remembered by a object-status fact
with a status present/not-present.
(defrule infer-object)
(logical (c (m ? ?x ?)))
=>
(assert (object ?x))
)
You'll have to use (logical (c (m ?$ ?x ?$))) or else it'll match only
lists with a length of three.
If an object gets removed from the list, the object-fact will
automatically be retracted. I'm not quite sure of the syntax though (it
has been a while). And I hope it works for templates with multi-slots.
(defrule object-status-present-first-time
(object ?x)
(not (object-status (obj ?x) (status ?s)))
=>
(assert (object-status (obj ?x) (status present)))
)
(defrule object-status-not-present
?os <- (object-status (obj ?x) (status p))
(not (object ?x))
=>
(modify ?os (status not_present))
)
(defrule object-status-present-again
(object ?x)
?os <- (object-status (obj ?x) (status not_present))
=>
(modify ?os (status present))
)
It seems that the object facts are retracted all right if some slot c.m
is reduced, but this does not trigger the second rule.
Also, note that if you change a multislot that contains, say (m x y) by
(modify ?some-c-fact (m x)), the final (object x) won't be the same
object as the original (object x). Both (object x) and (object y) are
thrown away, and then a new (object x) is created.
-WL
This way you only have to manipulate the c-template and a memory-
status will automatically be kept. The moment you react to the status-
changes depends on the salience of reaction-rules. (Similar to the rule
do-something-when-something-gets-removed-from-c)
I don't think this is very inefficient. Furthermore you don't need
cleanup rules, just three rules for administration purposes.
Martijn
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:owner-jess-
[EMAIL PROTECTED]
On Behalf Of Ernest Friedman-Hill
Sent: woensdag 20 februari 2008 13:31
To: jess-users
Subject: Re: JESS: Rules for detecting changes of a multislot
Lars,
If you think about it, there are only two ways to write a rule to
react to the absence of data:
1) Remember what the data was, so you can compare the present
situation to the previous situation;
2) Use a time machine, travel back in time, find out what the data
used to be, then come back to the present.
Of these, only #1 is practical to implement in software. :) This
isn't a problem with Rete; it's a problem with the fabric of reality.
Unfortunate, but it's something we've got to live with. Unless you
can come up with a way to build a time machine, you have to remember
the past if you're going to act on it.
But Martijn actually gave you two suggestions. The first one is my #1
above, which you've responded to as being inefficient.
The second one is not to react to changes, but to *participate* in
the changes, as they're happening. You need to make the changes
explicit. I don't think I'd do it quite the way that Martijn
suggests, though. But the basic idea is the same: it's too late to
react to the change after the change has been made; you have to react
to the change *while the change is being made.* For example, you
could use explicit command facts to remove items from the multislot,
and one or more rules to process the commands. So instead of saying
(defrule remove-something-from-c
?c <- (C (m ?a ?b ?c))
=>
(modify ?c (m ?a ?c)))
You'd say something like
(defrule want-to-remove-something-from-c
?c <- (C (m ?a ?b ?c))
=>
;; Instead of modifying ?c, issue a command to do so
(assert (remove ?c ?b)))
(defrule actually-remove-things-from-c
"Process commands to remove items from multislot m of C facts"
(declare (no-loop TRUE))
?c <- (C (m $?first ?x $?rest))
(remove ?c ?b)
=>
(modify ?c (m $?first $?rest)))
(defrule do-something-when-something-gets-removed-from-c
"This is the rule you were asking about how to write"
?c <- (C (m $?first ?x $?last))
(remove ?c ?x)
=>
(do whatever you want to do here))
(defrule clean-up-remove-commands
"A low salience rule to clean up remove commands when you're done
with them."
(declare (salience -1))
?r <- (remove ? ?)
=>
(retract ?r))
On Feb 20, 2008, at 5:09 AM, Lars Braubach wrote:
Hi,
thanks for your reply Martijn. The solution should work
but is also rather inefficient because all facts would have
be stored twice. Maybe some Rete expert could argue, if such
a rule could be expressed direcly in a rete network (not considering
the specification language). If this is possible it might indicate
that just the CLIPS/JESS language is insufficient for expressing
such
kind of behavior.
Kind regards,
Lars
Martijn Tromm schrieb:
Hi,
You must either keep the same data in another slot for reference
like:
(C (m a b c) (m-old a b c d)) Now you can compare old and new and
detect changes between. (actually you store the mutation this way)
Or I think you have to store each object in a separate fact and
keep track of changes through activations (addition) or
retractions and logical dependencies (removal).
Regards,
Martijn
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:owner-jess-
[EMAIL PROTECTED]
On Behalf Of Lars Braubach
Sent: dinsdag 19 februari 2008 10:34
To: [email protected]
Subject: JESS: Rules for detecting changes of a multislot
Hi,
I am trying to design a rule that is able to detect
when a single fact of a multislot is added/removed.
Given that the contained multislot values are
backed with Java objects I would also like to
know which fact has been added/removed.
(deftemplate C (multislot m))
(deffacts facts
(C (m a b c))
)
For the addition of values I could figure out
a rule that does what I want, but its unclear
to me how this could be achieved for the removal
of values. (The addition rule simply uses a pattern
(? ?fact ?) in order to generate bindings for
each element of the multislot.)
Any ideas how this could be achieved?
Kind regards,
Lars
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Ernest Friedman-Hill
Informatics & Decision Sciences Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
PO Box 969, MS 9012 [EMAIL PROTECTED]
Livermore, CA 94550 http://www.jessrules.com
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