COMP 4200: Expert Systems

1
COMP 4200 Expert Systems

• Dr. Christel Kemke
• Department of Computer Science
• University of Manitoba

2
CLIPS Introduction 2

• Review and Introduction 2
• CLIPS Programming System
• Basic CLIPS Constructs and Syntax
• Fields and Templates
• Complex Condition Patterns
• Input and Output
• Salience

3
CLIPS Programming Systems

• CLIPS Interpreter
• enter commands, direct modification of fact base
  ...
• CLIPS File-Menu
• load, save and edit CLIPS program files
• CLIPS Edit-Menu
• Balance (ctrl B), Comment
• CLIPS Execution-Menu
• set execution parameters (e.g. reset, run, clear,
  watch, constraint checking, halt)
• CLIPS Browse-Menu
• manage and info about constructs
• CLIPS Window-Menu
• current status info, e.g. Facts, Activations,

4
Working with Facts

• Changing fact base
• Adding facts (assert ltfactsgt)
• Deleting facts (retract ltfact-identifiergt)
• Modifying facts (modify ltfact-identifiergt
• (deftemplate facts) (ltslot-namegt ltslot-valuegt))
• Duplicating facts (duplicate ltfact-identifiergt
• (deftemplate facts) (ltslot-namegt
  ltslot-valuegt))
• Monitoring program execution
• Print all facts (facts)
• Displays changes (watch facts), also for rules
  ...
• Dribble record trace into file

5
CLIPS Basic Constructs

• Basic Language Elements
• Fields (basic Data Types slot fillers)
• Facts (used in condition patterns)
• Rules (condition-action rules)
• Templates (like records define facts)
• Classes (like objects define facts)
• Messagehandlers (like methods defined for
  classes used in condition patterns and
  actions)

6
Fields - Examples

• Fields (data types)
• float 4.00, 2.0e2, 2e-2
• integer 4, 2, 22
• symbol Alpha24, !?_at_
• string Johnny B. Good
• instance name titanic, PPK
• Variables
• ?var, ?x, ?day variables for single field value
• ?names variable for multi-field value

7
Template and Fact with Single Field

• Single value in a slot
• (person (name "Johnny B. Good" ) (age 42))
• Defined based on
• (deftemplate person
• (slot name)
• (slot age))
• A single field slot stores one single field
  value, e.g. the string "Johnny B. Good" or the
  integer / number 42 in the example above.

8
Multislots and Multifields

• More than one value in a slot
• (person (name Johnny B. Good) (age 42))
• Defined based on
• (deftemplate person
• (multislot name)
• (slot age))
• A multi-slot allows several field values to be
  stored in one slot, e.g. the 3 field values
  Johnny, B. and Good in the example above.

9
Slot Restrictions

• Defined Template with Slot-Restrictions
  (Constraint-Attributes)

(deftemplate person (slot name (type
STRING)) (slot age (type INTEGER)) (slot gender
(allowed-symbols male female)) )
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Slot Constraint-Attributes

• ltconstraint-attributegt lttype-attributegt 
• ltallowed-constant-attri
  butegt
• ltrange-attributegt
• ltcardinality-attributegt
  
• ltdefault-attributegt
• lttype-attributegt (type
  lttype-specificationgt )
• lttype-specificationgt ltallowed-typegt
  ?VARIABLE
• ltallowed-typegt SYMBOL STRING
  LEXEME
• INTEGER FLOAT
  NUMBER
• INSTANCE-NAME
  INSTANCE-ADDRESS
• INSTANCE
  FACT-ADDRESS
• EXTERNAL-ADDRESS

11
Slot Constraint-Attributes

• Type Allowed Values (Enumeration, Collection)
• ltallowed-constant-attributegt
• (allowedsymbols ltsymbol
  -listgt)
• (allowedstrings
  ltstring-listgt)
• (allowed-lexemes
  ltlexeme-listgt)
• (allowedintegers ltinteg
  er-listgt)
• (allowedfloats ltfloat-l
  istgt)
• (allowednumbers ltnumber
  -listgt)
• (allowed-instance-names
  ltinstance-listgt)
• (allowedvalues ltvalue-l
  istgt)

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Slot Constraint-Attributes

• Range of Values (min and max value)
• ltrange-attributegt (range
  ltrange-specificationgt ltrange-specification
  gt)
• ltrange-specificationgt ltnumbergt ?VARIABLE
• Number of Fillers (min and max)
• ltcardinality-attributegt (cardinality
• ltcardinality-specificationgt
• 
  ltcardinality-specificationgt)
• ltcardinality-specificationgt ltintegergt
  ?VARIABLE

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Variables and Wildcards

• single-field variable binds single value
• ?ltsymbolgt e.g. ?age, ?x, ?address
• ?fact-variable
• multi-field variable accepts multiple values
  ?ltsymbolgt can bind multi-field value
• single-field wildcard matches any single-field
  value
• ?
• multi-field wildcard matches any multi-field
  value
• ?

14
All Kinds of Variables

• (defrule birthday A persons birthday
• ?f1 lt- (person (name ?name) (age ?age))
• ?f2 lt- (has-birthday ?name)
• gt
• (printout t Happy Birthday, ?name)
• (retract ?f1)
• (retract ?f2)
• (assert (person (name ?name) (age ( ?age 1)))))

Q With which patterns does the Condition match?
A e.g. (person (name Johnny B. Good) (age 42))
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All Kinds of Variables 2

• (defrule birthday A persons birthday
• ?f1 lt- (person (name ?name ?) (age ?age))
• ?f2 lt- (has-birthday ?name)
• gt
• (printout t Happy Birthday, ?name)
• (retract ?f2)
• (modify ?f1 (age ( ?age 1))))

Q1 What is ? matching with? Q2 What is the
rule doing?
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Complex Condition Elements

• logical connectives and, or, not to combine
  patterns
• forall and exists consider all matches/ only
  one match in further evaluation
• logical connects condition element and asserted
  fact in action (Truth Maintenance)
• use test-condition
• (test ltpredicate-expressiongt)
• field-constraints , , and attached to slot
  of (deftemplate) condition pattern

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Field Constraints (Connected Pattern Constraints)

• not not this value
• (name Simpson)
• (age 40)
• or could be one of these values
• (name SimpsonOswald)
• (age 304050)
• and attaches constraint to variable
• (name ?nameSimpson)
• (name ?nameHarvey)
• expr. adds expression as constraint
• (age ?age(gt ?age 20))
• (name ?name(eq (sub-string 1 1 ?name) "S")

checks whether the age is above 20
checks whether the sub-string from 1 to 1 (first
letter) of the name is "S"
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Field Constraint

• (defrule you-wish something with people and age
• (person (name ?name) (age ?age(gt ?age 20))
• gt
• (printout t ?name is over twenty. crlf)
• (printout t ?name is ?age years old. crlf))

Q1 Which patterns match this Condition? Q2
What is the rule doing?
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Condition Patterns with Logical Connectives

• Complex Conditions with logical connectives
• (or (pattern1) (pattern2))
• Rule becomes active if one of the patterns
  matches.
• example (or (birthday) (anniversary))
• matches fact base with facts (birthday) or
  (anniversary)
• Equivalent for
• and (is default)
• not
• exists to be fulfilled for one matching fact
• forall to be fulfilled for all facts which match
  based on first fact and variable binding

20
Complex Condition Elements - or

• (defrule report-emergency
• (or (emergency (emergency-type fire) (location
  ?building))
• (emergency (emergency-type bomb) (location
  ?building))
• )
• gt
• (printout t evacuate ?building)
• )

reports a building if there is a fire or bomb
emergency in this building
21
Complex Condition Elements exists

• (defrule emergency-report
• (exists
• (or (emergency (emergency-type fire))
• (emergency (emergency-type bomb)))
• )
• gt
• (printout t There is an emergency. crlf )
• )

prints one emergency-message if there is a fire
or bomb emergency. (no further matching, firing,
or printout)
22
Complex Condition Elements forall

• (defrule evacuated-all-buildings
• (forall (emergency (emergency-type fire
  bomb)
• (location ?building) )
• (evacuated (building ?building)))
• gt
• (printout t All buildings with emergency are
  evacuated crlf))

prints evacuated-message if for all buildings,
which have a fire or bomb emergency, the building
is evacuated.
23
Exercise
(defrule special-age 18, 21, 100 (or (person
(name ?name) (age 18)) (person (name ?name)
(age 21)) (person (name ?name) (age
100))) gt (printout t ?name has a special
age.))
Task Modify the condition pattern so that you
use a variable for age, and field constraints for
the values, and printout the name and age of any
matching person.
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• (deftemplate person
• (slot age (type INTEGER))
• (multislot name (type STRING))
• (slot gender (allowed-values f m)) )
• (deffacts people
• (person (age 20) (name "Mike" "M." "Moore")
  (gender m))
• (person (age 40) (name "James" "J." "James" )
  (gender m))
• (person (age 42) (name "Susan" "D." "More")
  (gender f))
• (person (age 28) (name "John" "J." "Jones")
  (gender m)) )
• (defrule what-am-I-doing
• (or (person (name ?first ?middle ?last(eq
  ?last "Moore")))
• (person (name ?first ?middle ?last(eq
  ?last "More"))) )
• gt
• (printout t "Found " ?first " " ?last crlf) )

Q1 What is the rule doing?
Q2 Can you simplify the Condition Element? Do it!
25
bind-function

• bind-function explicitly binds value to
  variable
• (bind ?age (read))
• stores value of single field which is read into
  single-field variable ?age
• (bind ?name (readline))
• stores line which is read as STRING into
  single-field STRING-variable ?address
• (bind ?address (explode (readline)))
• explode splits line which is read as STRING into
  multifield-value which is stored in
  multislot-variable ?address

26
Open, Close File

• Open file for read/write
• (open ltfile-namegt ltlogical-namegt r)
• ltfile-namegt is physical file-name (path)
• ltlogical-namegt is name used in program
• r indicates read-access (w, r)
• example (open example.dat my-file r)
• (read my-file)
• Close file
• (close ltlogical-namegt)

27
Input read, readline

• read input of single field
• readline input of complete (line as string)
• general
• (read ltlogical namegt)
• ltlogical namegt refers to file-name in program
• (read) keyboard is default
• read with bind-function to bind input to
  variable
• (bind ?input (read))
• (bind ?input (readline))

28
Input read, readline

• (read / readline ltlogical namegt)
• default is keyboard/terminal
• file has to be opened using
• (open ltfile-namegt ltlogical-namegt r)
• ltfile-namegt is physical file-name (can include
  path)
• ltlogical-namegt is name used in read command
• r indicates read-access
• example (open example.dat example r)
• (read example)
• use with bind-function to bind input to variable

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Output - printout

• (printout ltlogical-namegt ... )
• t terminal is standard
• otherwise ltlogical-namegt refers to a file-name
• file has to be opened using
• (open ltfile-namegt ltlogical-namegt w )
• ltfile-namegt is physical file-name (can include
  path)
• ltlogical-namegt is name used in printout command
• w indicates write-access
• example (open example.dat my-output w )
• (printout my-output ?name crlf)

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Rules - Runtime Effects

• refraction
• each rule fires only once on the same data
• agenda
• rules are activated in sequence and put on
  agenda agenda is like a stack the last rule
  fires first
• salience
• sequence of rule firings - in case of a conflicts
  is determined by their set salience factor the
  higher the salience, the higher the rule priority

31
Rules - Salience
Rules defined with salience factor
(defrule say-hello (declare (salience
10)) (person (name ?name)) gt (printout t
Hello, ?name)) (defrule say-happy-birthday (de
clare (salience 100)) (person (name ?name))
gt (printout t Happy Birthday, ?name))
The higher the salience, the higher the rule
priority in conflict situations.