Artificial Intelligence CLIPS Language Tutorial

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Artificial IntelligenceCLIPS Language Tutorial

• Michael Scherger
• Department of Computer Science
• Kent State University

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Introduction

• CLIPS is a tool for building expert systems
• Originally developed by the Software Technology
  Branch (STB) at NASA Johnson Space Center
• First release in 1986
• Web location
• http//www.ghg.net/clips/CLIPS.html

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Introduction

• CLIPS was designed to facilitate the development
  of software to model human knowledge
• Facts
• Rules
• Deffunctions and generic functions
• Object oriented programming

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Starting / Exiting CLIPS

• To start CLIPS (Windows)just double click the
  CLIPSWin.exe icon
• To exit CLIPS type (exit) at the CLIPSgt prompt.

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Facts

• Fact Assertion
• (assert (play Ivan tennis))
• (assert (duck))
• (assert (chair red))
• As facts are entered into the KB, they are
  assigned a Fact Index
• (retract 1)
• Removes fact 1 from the KB
• (clear)
• Removes all facts from the fact base and KB

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Facts

• Fact Assertion
• (facts)
• Dump the fact base
• Fact identifier time tag
• f-0
• f-1
• Special fact
• (initial-fact)
• Is always F0 and is used to match the first/start
  rules

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Facts

• deffacts is a way of initializing the fact base
  (group of facts)
• Example
• (deffacts tennis-players people who play
  tennis
• (athelete Ivan very-good)
• (play Ivan tennis)
• (athelete Martina very-good)
• (play Martina tennis))
• Will cause the fact base to be initialized with
  the facts (initial-fact)

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Facts

• When (reset) is entered, the result is
• f-0 (initial-fact)
• f-1 (athelete Ivan very-good)
• f-2 (play Ivan tennis)
• f-3 (athelete Martina very-good)
• f-4 (play Martina tennis)

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Rules

• Syntax
• (defrule r-name comment
• pattern-1
• pattern-n
• gt
• action-1
• action-m)

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Rules

• r-name is the rule name
• comment must be surrounded by quotes
• pattern-i is the antecedent pattern
• action-j is the consequent pattern

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Rules

• The agenda is the list of rules that have been
  matched and are waiting execution
• (agenda) will print out the rules
• The agenda is prioritized by salience value
• Salience is specified by the programmer and is
  from -10000 to 10000
• Default is 0 if (declare (salience 25)) is not in
  rule e.g.
• Rules are selected for firing by salience
• Two rules of same salience use LIFO to fire

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Rules

• (pprule r-name) will pretty print out the rule
• (excise r-name) will remove a rule from the system

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Variables

• Variables start with a ?
• E.g. ?age
• Bindings are valid within a rule only

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Fact Base Updates

• (retract fact-id)
• requires fact to be the index number which is
  sometime difficult to determine
• Therefore use
• variable with lt- notation which binds the fact
  index number to the variable

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Fact Base Updates

• Example
• (defrule become-adult
• ?child lt- (child harry)
• (birthday harry August-15)
• ?age lt- (age harry 17)
• (date today August-15)
• gt
• (assert (adult harry))
• (retract ?child)
• (retract ?age)
• (assert (age harry 18))
• (printout t harry is now an adult crlf))

• What facts are retracted?
• What facts are kept?
• What facts are generated?
• Changing harry to ?person and August-15 to ?date
  will generalize this rule

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Firing Rules
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Firing Rules
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Firing Rules (Matching)
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Firing Rules (Matching)
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Wildcard Matching

• ?
• matches one
• ?
• matches any number
• ?name
• match and bind

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Variables, Variables, Variables

• Variables start with a ?
• Examples
• ?x ?sensor ?color
• ?location ?room ?size

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Variables, Variables, Variables
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Wildcard Matching

• Example
• (name ? ?Kennedy)
• will match
• (name John Fitzgerald Kennedy)
• (name ? ? SMITH)
• will match
• (name John SMITH)
• (name Suzie Jane SMITH)
• (name John James Jones SMITH)
• but would not match
• (name SMITH)
• (name John Jones SMITH Rogers)
• ?name is the same as the previous but the
  matches are bound to ?name

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Wildcard Matching
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Field Constraints

• Negation
• (defrule apply-heat
• (temperature water boil)
• gt
• (adjust heat maximum) a function call
• (printout t Turn the heat to the maximum
  setting crlf))

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Field Constraints

• OR
• (defrule apply-heat
• (temperature water coldcoolwarm)
• gt
• (adjust heat maximum) a function call
• (printout t Turn the heat to a medium setting
  crlf))

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Field Constraints

• AND
• (temperature water ?temphotboil)
• will match either of the following facts
• (temperature water hot)
• (temperature water boil)

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Mathematical Operators

• Uses prefix notation as in Lisp
• ( 3 4)
• ( ( 3 4) ( 5 6))
• Use as assignment for fact assertion on left
  hand side
• (assert (answer ( 3 4 ) ) )
• put
• (answer 12)
• in the fact list

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Systematic Manner
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Templates