Transcript 20 Lecture CSC462 x

Artificial Intelligence
Lecture No. 20
Dr. Asad Ali Safi
Assistant Professor,
Department of Computer Science,
COMSATS Institute of Information Technology (CIIT)
Islamabad, Pakistan.
Summary of Previous Lecture
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Reopen
Rule
Print out
Variables
Today’s Lecture
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Be Assertive
variable more than once
Retraction
single-field wildcard
Be Assertive
• One common use of variables is to match a
value on the LHS and then assert this bound
variable on the RHS. For example, enter
(defrule make-quack
(duck-sound ?sound)
=>
(assert (sound-is ?sound)))
variable more than once
• Be sure to do a (reset) and assert (duck-sound
quack) again.
(defrule make-quack
(duck-sound ?sound)
=>
(assert (sound-is ?sound ?sound)))
• When the rule fires, it will produce (sound-is
quack quack) since the variable ?sound is used
twice.
• (duckshoot ?hunter ?who)
CLIPS> (clear)
CLIPS> (defrule whohunt
(duckshoot ?hunter ?who)
=>
(printout t ?hunter " shot " ?who crlf))
(assert (duckshoot Brian duck))
Retraction
• Retraction is very useful in expert systems and
usually done on the RHS rather than at the
top-level. Before a fact can be retracted, it
must be specified to CLIPS. To retract a fact
from a rule, the fact-address first must be
bound to a variable on the LHS.
• However, if you want to remove the fact
whose contents are, you must first tell CLIPS
the address of the fact to be retracted.
• The fact-address is specified using the left
arrow, "<-". To create this, just type a "<“
symbol followed by a "-"
(defrule get-married
?Ad <- (bachelor Ali)
=>
(printout t “Ali is now happily married " ?Ad crlf)
(retract ?Ad))
(assert (bachelor Ali))
(run)
(defrule marriage
?Ad <- (bachelor ?name)
=>
(printout t ?name " is now happily married" crlf)
(retract ?Ad)
(deffacts good-prospects
(bachelor Ali)
(bachelor Aslam)
(bachelor Abid))
(reset)
(run)
Summery of Today’s Lecture
•
•
•
•
Be Assertive
variable more than once
Retraction
single-field wildcard