Introduction to CLIPS Expert System

CLIPS: Expert System Shell Motaz K. Saad College of IT – CS Dept.

What is expert system? AN EXPERT SYSTEM (ES) IS A COMPUTER PROGRAM DESIGNED TO SIMULATE THE PROBLEM-SOLVING BEHAVIOR OF AN EXPERT IN A NARROW DOMAIN OR DISCIPLINE.

What is expert system? ARTIFICIAL INTELLIGENCE PROGRAMS Exhibit intelligent behavior by skillful application of heuristics make domain knowledge explicit and separate from the rest of the system KNOWLEDGE-BASED SYSTEMS Apply expert knowledge to difficult, real world problems EXPERT SYSTEMS

The structure of an expert system KNOWLEDGE BASE Domain Knowledge INFERENCE ENGINE General problem-solving knowledge FACTS RULES INTERPRETER SCHEDULER

Facts and Rules A fact is a piece of information such as (color green) Facts on their own are of only limited use. The application of rules is necessary to develop a program capable of some useful function.

Rules A rule is a formal way of specifying a recommendation, directive, or advice A rule is expressed as IF premise THEN conclusion or IF condition THEN action

Drawing inferences from rules Forward chaining In forward chaining, the reasoning proceeds from the IF part of the rule to the THEN part. Backward chaining In backward chaining, the reasoning proceeds from the THEN part to the IF part.

Expert system building tool Programming language An expert system can be implemented using a general purpose programming language. However, the programming languages LISP and PROLOG are typically used in expert systems implementation, in particular Artificial Intelligence applications. This is due to their capabilities in handling symbolic data efficiently. Shells A shell consists mainly of an inference engine and an editor to assist developers in building their knowledge base.

Shells vs. Programming languages

CLIPS: Expert System Shell Rule-based expert systems are often known as production systems (CLIPS actually stands for C Language Integrated Production System).

The CLIPS Programming Tool History of CLIPS Influenced by OPS5 and ART Implemented in C for efficiency and portability Developed by NASA, distributed & supported by COSMIC Runs on PC, Mac, also under UNIX and VAX VMS CLIPS provides mechanisms for expert systems A top-level interpreter Production rule interpreter Object oriented programming language LISP-like procedural language

Components of CLIPS Rule-Based Language Can create a fact list Can create a rule set An inference engine matches facts against rules Object-Oriented Language Can define classes Can create different sets of instances Special forms allow you to interface rules and objects

Defining Facts Facts can be asserted CLIPS> (assert (today is sunday)) <Fact-0> Facts can be listed CLIPS> (facts) f-0 (today is sunday) Facts can be retracted CLIPS> (retract 0) CLIPS> (facts)

Managing Facts Clearing all facts CLIPS> (clear) CLIPS> (facts) Grouping facts - typically in a file (“today.clp”) (deffacts today ; can be cleared with (undeffacts today) (today is sunday) (weather is warm) ) After loading facts, assert with (reset)

Defining Rules Rules have the following structure (defrule rule-name optional-comment optional-declaration condition ... condition => action ... action )

An Example CLIPS Rule (defrule sunday “Things to do on Sunday” (salience 0) ; salience in the interval [-10000, 10000] (today is Sunday) (weather is sunny) => (assert (chore wash car)) (assert (chore chop wood)) ) So, if fact list contains conditions, add assertions

Getting the Rules Started The reset command creates a special fact CLIPS> (load “today.clp”) CLIPS> (facts) CLIPS> (reset) CLIPS> (facts) f-0 (initial-fact) ... (defrule start (initial-fact) => (printout t “hello”) )

Tracing & Recording Things Watch command can watch facts (and rules) CLIPS> (watch facts) CLIPS> (reset) ==> f-0 (initial-fact) CLIPS> (retract 0) <== f-0 (initial-fact) Contents of dialog window can be sent to file CLIPS> (dribble-on “dribble.clp”) ; any file name will do ... CLIPS> (dribble-off “dribble.clp”)

Variables & Pattern Matching Variables make rules more applicable (defrule pick-a-chore (today is ?day) (chore is ?job) => (assert (do ?job on ?day)) ) If conditions are matched, then bindings are used

Retracting Facts from a Rule (defrule do-a-chore (today is ?day) ; ?day must have a consistent binding ?chore <- (do ?job on ?day) => (printout t ?job “ done”) (retract ?chore) ) We must assign a variable to item for retraction

Pattern Matching Details One-to-one matching (do ?job on ?day) (do washing on monday) Use of wild cards (do ? ? monday) (do ? on ?) (do ? ? ?day) (do $?) (do $? monday) (do ?chore $?when)

Using Templates (deftemplate student “a student record” (slot name (type STRING)) (slot age (type NUMBER) (default 18))) CLIPS> (assert (student (name fred))) (defrule print-a-student (student (name ?name) (age ?age)) => (printout t name? “ is “ ?age) )

Defining Functions in CLIPS Uses a LISP or Scheme-like syntax (deffunction function-name (arg ... arg) action ... action) (deffunction hypotenuse (?a ?b) (sqrt (+ (* ?a ?a) (* ?b ?b)))) (deffunction initialize () (clear) (assert (today is sunday)))

Defining Classes & Instances Defining the class CAR (defclass car (is-a user) (name) (made-by)) Defining an instance of CAR (make-instance corvette of car (made-by chevrolet))

Concrete & Abstract Classes Some classes only exist for inheritance purposes Person Man Woman Jack Jill

Managing Instances Commands to display instances CLIPS> (instances) [corvette] of car CLIPS> (send [corvette] print) [corvette] of car (made-by chevrolet) Command to group instances (in a file) (definstances (corvette of car (made-by chevrolet)) (thunderbird of car (made-by ford)))

Clearing & Resetting Instances Deleting an instance CLIPS> (send [corvette] delete) Deleting all instances CLIPS> (unmake-instance *) Resetting creates an initial object CLIPS> (reset) CLIPS> (instances) [initial-object] of INITIAL-OBJECT

Message Passing The SEND function (send [instance] message arg ... arg) Converting from symbols to names CLIPS> (symbol-to-instance-name corvette) [corvette] This is useful when SENDing from inside a rule

Limitations of CLIPS Single level rule sets in LOOPS, you could arrange rule sets in a hierarchy, embedding one rule set inside another Loose coupling of rules and objects rules can communicate with objects via message passing rules cannot easily be embedded in objects, as in Centaur CLIPS has no explicit agenda mechanism the basic control flow is forward chaining to implement other kinds of reasoning you have to manipulate tokens in working memory

Alternatives to CLIPS Eclipse has same syntax as CLIPS (both are based on ART) supports goal-driven (i.e., backwards) reasoning has a truth maintenance facility for checking consistency can be integrated with C++ and dBase new extension RETE++ can generate C++ header files NEXPERT OBJECT another rule- and object-based system has facilities for designing graphical interfaces has a ‘script language’ for designing user front-end written in C, runs on many platforms, highly portable

The End! http://motaz.saad.googlepages.com

Introduction to CLIPS Expert System

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Introduction to CLIPS Expert System