230639

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http://slidepdf.com/reader/full/230639 1/62

Seyed Hashem Davarpanah

[email protected] of Science and

Culture

Expert systemsCLIPS

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otivation

• CLIPS is a decent example of anexpert system shell– rule!"ased# for$ard!chainin% system

• it illustrates many of the conceptsand methods used in other &PS shells

• it allo$s the representation of'no$led%e# and its use for solvin%suita"le pro"lems

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Introduction

• CLIPS stands for– C Lan%ua%e Implementation Production

System

• for$ard!chainin%– startin% from the facts# a solution is

developed

• pattern!matchin%– (ete matchin% al%orithm) find **fittin%++

rules and facts• 'no$led%e!"ased system shell

– empty tool# to "e filled $ith 'no$led%e

• multi!paradi%m pro%rammin% lan%ua%e– rule!"ased# o",ect!oriented -Cool and

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(ete atchin% /l%orithm

• /n expert system mi%ht chec' each rule a%ainst the'no$n facts in the 'no$led%e "ase# firin% that rule ifnecessary# then movin% on to the next rule.

• 0or even moderate si1ed rules and facts 'no$led%e!"ases# this approach performs far too slo$ly.

• 2he (ete al%orithm provides the "asis for a moreefficient implementation.

• / (ete!"ased expert system "uilds a net$or' ofnodes# $here each node -except the root correspondsto a pattern occurrin% in the left!hand!side -thecondition part of a rule.

• 2he path from the root node to a leaf node defines a

complete rule left!hand!side. Each node has a memoryof facts $hich satisfy that pattern. /s ne$ facts areasserted or modified# they propa%ate alon% thenet$or'# causin% nodes to "e annotated $hen thatfact matches that pattern. 3hen a fact or com"inationof facts causes all of the patterns for a %iven rule to "esatisfied# a leaf node is reached and the correspondin%rule is tri%%ered.

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2he CLIPS Pro%rammin% 2ool

• history of CLIPS– influenced "y 4PS5 and /(2– implemented in C for efficiency and

porta"ility

– developed "y 6/S/# distri"uted 7supported "y C4SIC– runs on PC# ac# U6I&# 8/& 8S

• CLIPS provides mechanisms for expertsystems– a top!level interpreter– production rule interpreter– o",ect oriented pro%rammin% lan%ua%e

– LISP!li'e procedural lan%ua%e

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Components of CLIPS

• rule!"ased lan%ua%e– can create a fact list– can create a rule set

– an inference en%ine matches factsa%ainst rules

• o",ect!oriented lan%ua%e -C44L

– can define classes– can create different sets of instances– special forms allo$ you to interface

rules and o",ects

[Jackson 1999]

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6otation• sym"ols# characters# 'ey$ords

– entered exactly as sho$n)– (example)

• s9uare "rac'ets [...]– contents are optional)– (example [test])

• pointed "rac'ets -less than : %reater than si%ns < ... >– replace contents "y an instance of that type– (example <char>)

• star * – replace $ith 1ero or more instances of the type– <char>*

• plus + – replace $ith one or more instances of the type– <char>+ -is e9uivalent to <char> <char>*

• vertical "ar | – choice amon% a set of items)

– true | false

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Invo'e : Exit CLIPS

• enterin% CLIPSdou"le!clic' on icon# or type pro%ram name

-CLIPS

system prompt appears) CLIPS>

• exitin% CLIPSat the system prompt

CLIPS> type (exit)

– 6ote) enclosin% parentheses are important;they indicate a command to "e executed#not ,ust a sym"ol

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0ields ! Examples

0ields -data types• float <.==# >.=e?># >e!>

• inte%er <# ># >>

• sym"ol /lpha><# AB@

• strin% ohnny F. Good

• instance name titanicJ# PPKJ

8aria"lesBvar# Bx# Bday varia"les for sin%le field value

Bnames varia"le for multi!field value

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CLIPS 0acts

0acts• a relation!name#• an ordered se9uence of values -ordered

facts# or• a set of -slot!name slot!value!pairs -i.e.deftemplate!facts

examples)

-today is 2hursday-person -name ohnny F. Good -a%e >5

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4rdered 0acts

4rdered facts• are facts defined $ithout -explicit template;• the field!values are ordered.

Examples)

-num"er!list M > 55 N O <>

-today is Sunday

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Deftemplate 0acts

Deftemplate!facts

• are facts defined "ased on atemplate;

• slots can "e arran%ed ar"itrarily#there is no specific order.

•Define a template for descri"in% aset of facts usin% deftemplate -recordstructure .

• Use deffacts to create a list of facts

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Examples of 0acts

• ordered fact(perso!ame "ra# $. %urfess)

• deftemplate fact(&eftemplate perso '&eftemplateexample

(slot ame)

(slot ae) (slot ee!color)

(slot hair!color))

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Instances

• an instance of a fact is created "y

(assert (perso (ame '"ra# $.

%urfess')

(ae ,-)

(ee!color ro/)

(hair!color ro/))

)

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Initial 0acts

(&effacts 0urfesses 'some memers of the %urfessfamil'

(perso (ame '"ra# $. %urfess') (ae ,-)

(ee!color ro/) (hair!colorro/))

(perso (ame '1uert %urfess') (ae ,,) (ee!color lue) (hair!color lo&))

(perso (ame '2erhar& %urfess') (ae ,3)

(ee!color lue) (hair!color lo&))

(perso (ame '1eirich %urfess') (ae 45)

(ee!color ro/) (hair!colorlo&))

(perso (ame 'Irmar& %urfess') (ae 46)

(ee!color ree) (hair!colorlo&))

)

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Usa%e of 0acts

• addin% facts– (assert <fact>+)

• deletin% facts– (retract <fact!i&ex>+)

• modifyin% facts– (mo&if <fact!i&ex> (<slot!ame> <slot!7alue>)+ )

• retracts the ori%inal fact and asserts a ne$# modified fact

• duplicatin% facts– (&uplicate <fact!i&ex> (<slot!ame> <slot!7alue>)+ )

• adds a ne$# possi"ly modified fact

• inspection of facts– (facts)

• prints the list of facts

– (/atch facts)

• automatically displays chan%es to the fact list

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(ules

• %eneral format(&efrule <rule ame> ['commet']

<patters>* 8 left!ha& si&e (L1S)

8 or atece&et ofthe rule

9>

<actios>*) 8 riht!ha& si&e

(:1S)8 or cose;uet of

the rule

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(ule Components

• rule header– defrule 'ey$ord# name of the rule#

optional comment strin%

• rule antecedent -LHS– patterns to "e matched a%ainst facts

• rule arro$

– separates antecedent and conse9uent• rule conse9uent -(HS

– actions to "e performed $hen the rulefires

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(ule ! Example

-defrule "irthday / persons "irthday-person -name Bname -a%e B

a%e-has!"irthday Bname Ba%e

QR

-printout t Happy Firthday# Bname

template

fact

ordered

fact

terminal

rule name comment

variables

variabletextfunction

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Examples of (ules

• simple rule(&efrule irth&a!"$%

(perso (ame '"ra# $.%urfess')

(ae ,-) (ee!color ro/)

(hair!color ro/))

(&ate!to&a pril!34!=)

9>

(pritout t '1app irth&a "ra#?')

(mo&if 3 (ae ,6))

)

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3ildcards

• 9uestion mar' @

– matches any sin%le field $ithin a fact

• multi!field $ildcard A@ – matches 1ero or more fields in a fact

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Salience

• 3e can use salience measures to prioriti1erules.

• CLIPS provides a "uilt!in method for

prioriti1in% rules)-declare -salience value

• Salience values can ran%e from !M==== to?M====. Default is =.

• 3e can thus force the execution of one ruleover another. 3e can implement se9uencin%of rules.

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(ule Prioriti1ation in Clips

• for example# consider the follo$in%rules... -forced order of execution

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2$o 6ifty (ules

-defrule fire!first-declare -salience =-priority first

QR-printout t TPrint 0irstT crlf

-defrule fire!second

-declare -salience >=-priority secondQR

-printout t TPrint SecondT crlf

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0ield Constraints

• not constraint B– the field can ta'e any value except the one

specified

• or constraint |– specifies alternative values# one of $hich

must match

• and constraint – the value of the field must match all

specified values

– mostly used to place constraints on the

"indin% of a varia"le

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athematical 4perators

• "asic operators -+!*D) and many functions-tri%onometric# lo%arithmic# exponential aresupported

• prefix notation

• no "uilt!in precedence# only left!to!ri%ht andparentheses• test feature

– evaluates an expression in the LHS instead of matchin% apattern a%ainst a fact

• pattern connectives– multiple patterns in the LHS are implicitly EF!connected– patterns can also "e explicitly connected via EF G: EGH

• user!defined functions– external functions $ritten in C or other lan%ua%es can "e

inte%rated

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Example (ule $ith 0ieldConstraints

(&efrule sill!ee!hair!match(perso (ame @ame3)

(ee!color @ees3lue|ree)

(hair!color @hair3Blac0))

(perso (ame @ame=B@ame3)(ee!color @ees=B@ees3)

(hair!color @hair=re&|@hair3))

9>

(pritout t @ame3 ' has '@ees3 'ees a& ' @hair3 ' hair.' crlf)

(pritout t @ame= ' has '@ees= 'ees a& ' @hair= ' hair.' crlf))

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Usin% 2emplates

(&eftemplate stu&et a stu&et recor&

(slot ame (tpe SH:IEJ))

(slot ae (tpe EK2M:) (&efault 35)))

CLIPS> (assert (stu&et (ame fre&)))

(&efrule prit!a!stu&et

(stu&et (ame @ame) (ae @ae))

9>(pritout t @ame is @ae)

)

[Jackson 1999]

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/n Example CLIPS (ule

(&efrule su&a Hhis to &o o Su&a

(saliece ) 8 saliece i the iter7al [!

3 3]

(to&a is Su&a)

(/eather is su)

9>

(assert (chore /ash car))

(assert (chore chop /oo&))

)

[Jackson 1999]

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8aria"les 7 Patternatchin%

• 8aria"les ma'e rules more applica"le

(&efrule pic0!a!chore

(to&a is @&a)

(chore is @No)9>

(assert (&o @No o @&a)))

• if conditions are matched# then"indin%s are used

[Jackson 1999]

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(etractin% 0acts from a (ule

(&efrule &o!a!chore

(to&a is @&a) 8 @&a must ha7e acosistet i&i

@chore <! (&o @No o @&a)

9>(pritout t @No &oe)

(retract @chore))

• a varia"le must "e assi%ned to the itemfor retraction

[Jackson 1999]

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Procedural Control in /ctions

• Procedural Control Elements canappear on the (HS of a rule or inmessa%e!handlers of classes.

(if <predicate-expression>ten <expression>!

[else <expression>! ]" ##else-part optional

( $ile <predicate-expression>

[do] <expression>* ]" ##%do’ not mandatory

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Example if!then!else

(defrule special-a&e '1) *1) 1++,(or (person (name name" (a&e a&e.1""

(person (name name" (a&e a&e.*1""

(person (name name" (a&e a&e.1++"""

/>(if (/ a&e 1" ten (printout t name ' can bu0 beer

in anada2,"

else

(if (/ a&e *1" ten (printout t name ' can

bu0 beer in te 3452,"

else

(if (/ a&e 1++" ten (printout t '6e

ma7or $ill visit , name ""222"

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Complex Condition Elements ! or

-defrule report!emer%ency

-or -emer%ency -emer%ency!type fire -location B

"uildin%

-emer%ency -emer%ency!type "om" -location B

"uildin%

QR-printout t evacuate B"uildin%

reports a building if there is a fire or bomb emergencyin this building

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Complex Condition Elements forall

-defrule evacuated!all!"uildin%s -forall -emer%ency -emer%ency!type fire "om"

-location B"uildin% -evacuated -"uildin% B"uildin%

QR-printout t /ll "uildin%s $ith emer%ency areevacuated crlf

prints evacuated-message if for all buildings, which have a

fire or bomb emergency, the building is evacuated.

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Salience

• 3e can use salience measures to prioriti1erules.

• CLIPS provides a "uilt!in method for

prioriti1in% rules)-declare -salience value

• Salience values can ran%e from !M==== to?M====. Default is =.

• 3e can thus force the execution of one ruleover another. 3e can implement se9uencin%of rules.

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2$o 6ifty (ules

-defrule fire!first-declare -salience =-priority first

QR-printout t TPrint 0irstT crlf

-defrule fire!second

-declare -salience >=-priority secondQR

-printout t TPrint SecondT crlf

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anipulation of Constructs

• sho$ list of constructs(list!&efrules) (list!&eftemplates) (list!&effacts)

• prints a list of the respective constructs

• sho$ text of constructs

(pp&efrule <&efrule!ame>) (pp&eftemplate<&eftemplate!ame>) (pp&effacts <&effacts!ame>)• displays the text of the construct -**pretty print++

• deletin% constructs(u&efrule <&efrule!ame>) (u&eftemplate<&eftemplate!ame>) (u&effacts <&effacts!ame>)

• deletes the construct -if it is not in use• clearin% the CLIPS environment

(clear) • removes all constructs and adds the initial facts to the CLIPS

environment

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"ind!function

"ind!function explicitly "inds value tovaria"le

-"ind Ba%e -read

stores value of sin%le field $hich is read

into sin%le!field varia"le Ba%e-"ind Bname -readline

stores line $hich is read as S2(I6G into

sin%le!field S2(I6G!varia"le Baddress-"ind Baddress -explode -readline

explode splits line $hich is read as S2(I6G

into multifield!value $hich is stored in

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4pen# Close 0ile

4pen file for read:$rite)-open Vfile!nameR Vlo%ical!nameR r

– Vfile!nameR is physical file!name -path

– Vlo%ical!nameR is name used in pro%ram

– r indicates read!access -$# r?

example) -open example.dat my!file r

-read my!file

Close file)-close Vlo%ical!nameR

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Input read# readline

-read : readline Vlo%ical nameR– default is 'ey"oard:terminal

– file has to "e opened usin%

-open Vfile!nameR Vlo%ical!nameRr• Vfile!nameR is physical file!name -can

include path

• Vlo%ical!nameR is name used in readcommand

• r indicates read!access

example) -open example.dat example r

-read example

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4utput ! printout

-printout Vlo%ical!nameR ... W t terminal is standard

other$ise Vlo%ical!nameR refers to a file!name

file has to "e opened usin%

-open Vfile!nameR Vlo%ical!nameR $

– Vfile!nameR is physical file!name -caninclude path

– Vlo%ical!nameR is name used inprintout command

W $ indicates $rite!access

example) -open example.dat my!output $

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Pro%ram Execution

• a%enda– if all patterns of a rule match $ith facts# it is

put on the a%enda– (ae&a) displays all activated rules

• salience– indicates priority of rules

• refraction

– rules fire only once for a specific set of facts• prevents infinite loops

– (refresh <rule!ame>) • reactivates rules

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Execution of a Pro%ram

• (reset) prepares -restart of a pro%ram)– all previous facts are deleted– initial facts are asserted– rules matchin% these facts are put on the

a%enda• (ru [<limit>]) starts the execution• "rea'points

– (set!rea0 [<rule!ame>])• stops the execution "efore the rule fires#• continue $ith -ru

– (remo7e!rea0 [<rule!ame>])

– (sho/!rea0s)

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3atchin%

• $atchin% the execution– (/atch </atch!item>) prints messa%es

a"out activities concernin% a </atch!

item>• (facts rules acti7atios

statistics compilatio focus all)

– (u/atch </atch!item>) • turns the messa%es off

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3atchin% 0acts# (ules and /ctivations

• facts– assertions -add and retractions -delete

– of facts

• rules– messa%e for each rule that is fired

• activations– activated rules) matchin% antecedents

– these rules are on the a%enda

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ore 3atchin% ...• statistics

– information a"out the pro%ram execution– -num"er of rules fired# run time# ...

• compilation -default– sho$s information for constructs loaded "y(loa&)

• Fefii &eftemplateO ...• Fefii &efruleO ... +N9N

– ?,# Q, indicates the internal structure of the compiledrules

8 ?, ,oin added8 Q, ,oin shared

– important for the efficiency of the (ete pattern matchin%net$or'

• focus

– used $ith modules

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Definin% 0unctions in CLIPS

• Uses a LISP or Scheme!li'e syntax

(&effuctio fuctio!ame (ar ... ar)

actio ... actio)

(&effuctio hpoteuse (@a @)

(s;rt (+ (* @a @a) (* @ @))))

(&effuctio iitiali#e ()(clear)

(assert (to&a is su&a)))

[Jackson 1999]

Definin% Classes 7

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Definin% Classes 7Instances

• definin% the class C/((&efclass car

(is!a user)

(ame)(ma&e!))

• definin% an instance of C/((ma0e!istace cor7ette of car

(ma&e! che7rolet))

[Jackson 1999]

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ana%in% Instances

• Commands to display instancesCLIPS> (istaces)

[cor7ette] of car

CLIPS> (se& [cor7ette] prit)

[cor7ette] of car(ma&e! che7rolet)

• Command to %roup instances -in a file(&efistaces

(cor7ette of car (ma&e! che7rolet))

(thu&erir& of car (ma&e! for&)))

[Jackson 1999]

Clearin% 7 (esettin%

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Clearin% 7 (esettin%Instances

• deletin% an instanceCLIPS> (se& [cor7ette] &elete)

• deletin% all instancesCLIPS> (uma0e!istace *)

• resettin% creates an initial o",ect

CLIPS> (reset)CLIPS> (istaces)

[iitial!oNect] of IEIHIL!G2$MCH

[Jackson 1999]

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l i

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/lternatives to CLIPS

• ESS

– see "elo$• Eclipse

– enhanced# commercial variant of CLIPS– has same syntax as CLIPS -"oth are "ased on /(2– supports %oal!driven -i.e.# "ac'$ards reasonin%

– has a truth maintenance facility for chec'in% consistency– can "e inte%rated $ith C?? and dFase– ne$ extension (E2E?? can %enerate C?? header files– not related to the -ne$er IF Eclipse environment

• 6E&PE(2 4FEC2

– another rule! and o",ect!"ased system– has facilities for desi%nin% %raphical interfaces– has a Xscript lan%ua%e for desi%nin% user front!end– $ritten in C# runs on many platforms# hi%hly porta"le

[Jackson 1999]

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ESS

• ESS stands for ava Expert SystemShell

• it uses the same syntax and a lar%ema,ority of the features of CLIPS

• ti%ht inte%ration $ith ava– can "e invo'ed easily from ava pro%rams– can utili1e o",ect!oriented aspects of ava

•some incompati"ilities $ith CLIPS– C44L replaced "y ava classes– a fe$ missin% constructs

• more and more added as ne$ versions of ESSare released

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CLIPS Summary

• notation– similar to Lisp# re%ular expressions

• facts– (&eftemplate) (&effacts) assert D retract

• rules

– (&efrule ...)# a%enda• varia"les# operators# functions

– advanced pattern matchin%

• input:output– (pritout ...) (rea& ...) (loa& ...)

• pro%ram execution– (reset) (ru) rea0poits

• user interface– command line or GUI

Important Concepts and

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Important Concepts and 2erms

– a%enda– antecedent– assert– "ac'$ard chainin%– conse9uent– CLIPS

– expert system shell– fact– field– for$ard chainin%– function– inference– inference mechanism– instance– If!2hen rules– ESS

– 'no$led%e "ase– 'no$led%e

representation– pattern matchin%– refraction

– retract– rule– rule header– salience– template– varia"le– $ild card

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