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CLIPSProgramming3

ModularDesign,Execution

Control,andRuleEfficiency

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CLIPSprovi esanum ero s otattri utest atcan especi ie w ena

deftemplatesslotsaredefined.

Itis ossibletodefinetheallowedt esandvaluesthatcanbestoredina

slot.

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T etypeattri ute e inest e atatypest atcan ep ace inas ot.

Thegeneralformatofthetypeattributeis

t e

whereiseither

?VARIABLEor

SYMBOL,

STRING,

LEXEME,

INTEGER,

FLOAT,

NUMBER,

INSTANCENAME

INSTANCEADDRESS,

INSTANCE, FACTADDRESS,or

- .

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xamp e:

( def t empl at e per son

( mul t i sl ot name ( t ype SYMBOL) )( sl ot age ( t ype I NTEGER) ) )

Forexample,assigningthesymbolfourtotheageslotratherthanthe

integer4will

cause

an

error

as

shown:

CLI PS> ( asser t ( per son ( name Fr ed Smi t h)

[CSTRNCHK1] Aliteralslotvaluefoundintheassertcommanddoesnotmatchtheallowedtypesforslotage.

>

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CLIPSa soa owsyoutospeci ya isto a owe va ues oraspeci ictype.

Forexample,ifagenderslotisaddedtothepersondeftemplate,the

alloweds mbolsforthatslotcanberestrictedtomaleand emale:

( def t empl at e per son(

mul t i sl ot name ( t ype SYMBOL) )

sl ot a e t e I NTEGER

( sl ot gender ( t ype SYMBOL)( al l owed- symbol s mal e f emal e) ) )

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erearee g eren a owe va uea r u esprov e y :

allowedsymbols,allowedstrings,allowedLexemes,allowedintegers,allowedfloats,

allowednumbers,

allowed

instance

names,

and

allowed

values.

,genderslottobeingasymbol.

Itmerelyindicatesthatiftheslotsvalueisasymbol,thenitmustbeoneofthetwos mbols:eithermaleor emale.

Anystring,

integer,

or

float

would

be

alegal

value

for

the

gender

slot

if

the

(typeSYMBOL)attributewereremoved

Theallowedvaluesattributecanbeusedtocom letel restrictthesetofallowedvaluesforaslottoaspecifiedlist.

( def t empl at e per son

( mul t i sl ot name ( t ype SYMBOL) )( sl ot age ( t ype I NTEGER) )( sl ot gender ( al l owed- val ues mal e f emal e) ) )

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T erangeattri utea owst especi icationo minimuman maximum

numericvalues.

The eneralformatoftheran eattributeis

(range)

whereandareeither?VARlABLEoranumeric

.

Example:

( def t empl at e per son

( mul t i sl ot name ( t ype SYMBOL) )

( sl ot age ( t ype I NTEGER) ( r ange 0 ?VARI ABLE) ) )

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maximumnumberofvaluesthatcanbestoredinamultislot.

Thegeneral

format

of

the

cardinality

attribute

is

- - whereandareeither?VARIABLEorapositive

integer.

, ,

valuecontained

in

amultislot.

Example:

( def t em l at e vol l e bal l - t eam( sl ot name ( t ype STRI NG) )( mul t i sl ot pl ayer s ( t ype STRI NG)

( car di nal i t y 6 6) )( mul t i sl ot al t er nat es ( t ype STRI NG)

( car di nal i t y 0 2) ) )

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so enconven en oau oma ca y aveaspec e va ues ore naslotifnovalueisexplicitlystatedinanassertcommand.

Thegeneral

format

of

the

default

attribute

is

(default)

whereiseither?DERIVE,?NONE,asingleexpression(forasinglefieldslot),orzeroormoreexpressions(foramultifieldslot).

If

the

default

attribute

is

not

specified

for

a

slot,

then

it

is

assumed

to

be

(default?DERIVE).

Forasinglefieldslot,thismeansthatavalueisselectedthatsatisfiesthetype,range,andallowedvaluesattributesfortheslot.

Thederiveddefaultvalueforamultifieldslotwillbealistofidenticalvalues

thatare

the

minimum

allowed

cardinality

for

the

slot

(zero

by

default).

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nexamp eo er ve va ues s e o ow ng:CLI PS> ( cl ear )

CLI PS> ( def t empl at e exampl e

( s l ot a)

( sl ot b ( t ype I NTEGER) )

( sl ot c ( al l owed- val ues r ed gr een bl ue) )

( mul t i s l ot d)

( mul t i s l ot e ( car di nal i t y 2 2)

( t ype FLOAT)

( r ange 3. 5 l 0. 0) ) )

CLI PS> ( asser t ( exampl e) )

CLI PS> ( f act s)

f 0 ( exampl e ( a ni l )

( b 0)

(c red)

( d)

( e 3. 5 3. 5) )

For a t ot al of 1 f act.

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.whenthefactisasserted.

CLI PS> cl earCLI PS>( def t empl at e exampl e( sl ot a)

( sl ot b ( def aul t ?NONE) ) )CLI PS> ( asser t ( exampl e) )[ TMPLTRHS1] Sl ot b r equi r es a val ue because of i t s( def aul t ?NONE) at t r i but e.CLI PS> ( asser t ( exampl e ( b 1) ) )

CLI PS> ( f act s)f - 0 ( exampl e ( a ni l ) ( b 1) )For a t ot al of 1 f act .LI PS>

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:

CLI PS> ( cl ear )

CLI PS>

( sl ot a ( def aul t 3) )( sl ot b ( def aul t ( + 3 4) ) )

( mul t i sl ot d ( def aul t ( + 1 2) ( + 3 4) ) ) )CLI PS> ( asser t ( exampl e) ) ( f act s)f - 0 ( exampl e ( a 3) ( b 7) ( c a b c) ( d 3 7) )

For a t ot al of 1 f act .CLI PS>

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New unctionsare e ine usingt e e unctionconstruct.

Thegeneralformatofadeffunctionis:

- -

( r egul ar - par amet er >* [ ] )

*)

ere regu arparame er sas ng e e var a ean w car

parameter>is

amultifield

variable.

Thenameofthedeffunction,,mustbedistinct.

Thebodyofthedeffunction,representedby*,isaseriesof

expressionssimilartotheRHSofarulethatareexecutedinorderwhenthe

deffunctionis

called.

Unlikepredefinedfunctions,deffunctionscanbedeletedandthewatch

commandcanbeusedtotracetheirexecution.

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T ean ec arat ons

Specifytheargumentsthatwillbepassedintothedeffunctionwhenitis

called.

Adeffunctioncanreturnvalues.

Thereturnvalueisthatvalueofthelastexpressionevaluatedwithinthebody

of the deffunction.

E.g.( def f unct i on hypot enuse- l engt h ( ?a ?b)

( ** ( + ( * ?a ?a) ( * ?b ?b) ) 0. 5) )

Wherethe**functionwithitssecondargumentof0.5

computethe

square

root

(**)isthefirstargumentraised

tothepowerofthesecondargument

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Itcan eca e romt ecomman prompt:

CLI PS> ( hypot enuse- l engt h 3 4)

.

CLI PS>

Inamorereadableformat:

( def f unct i on hypot enuse- l engt h ( ?a ?b)( bi nd ?t emp ( + ( * ?a ?a) ( * ?b ?b) ) )

emp .

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e e urn unc on

Itallowsthecurrentlyexecutingdeffunctiontobeterminated.

Itssyntax

for

use

with

deffunctions:

( r et ur n [ ] )

Ifisspecified,theresultofitsevaluationisusedasthereturnvalue.

E.g.

( def f unct i on hypot enuse- l engt h ( ?a ?b)

( bi nd ?t emp ( + ( * ?a ?a) ( * ?b ?b) ) )

( r et ur n ( ** ?t emp 0. 5) ) )

OR

( def f unct i on hypot enuse- l engt h ( ?a ?b)( bi nd ?t emp ( + ( * ?a ?a) ( * ?b ?b) ) )

( bi nd ?c ( ** ?t emp 0. 5) )

r et ur n ?c

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Watc ingDe unctions

Whendeffunctionsarewatchedusingwatchcommand,aninformational

messageis

printed

whenever

adeffuction

begins

or

ends

execution.

CLI PS> ( wat ch def f ucnt i ons)

CLI PS> ( unwat ch def f unct i ons)

Watchspecificdeffucntions

CLI PS> ( wat ch def f ucnt i ons hypot enuse- l engt h)

CLI PS>

Wildcardparameter

Ifthelastparameterdeclaredinadeffunctionisamultifieldvariable,whichis

,

moreargumentsthanarespecifiedintheparameterlist.

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De unctioncomman s

Displaythetextrepresentationsofadeffunction:

deffunction

Deleteadeffunction:

(undeffunction)

sp ay e s o e unc ons e n e :

(listdeffunctions

[])

Returnsamultifieldvaluecontainningthelistofdeffucntions.

(getdeffunctionlist[])

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G o a varia es:

CLIPSallowsonetodefinevariablesthatretaintheirvaluesoutsidethescope

ofaconstruct

Localvariables:

(defruleexample1

data1?x

=>(printoutt?x=?xcrlf))

defrule exam le1

(data2?x)

=>

=

Thevalueof?xinruleexample1doesnotconstraininanywaythevalueof?xin

ruleexample2.

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T egenera ormato a e g o a is:

(defglobal[]*)

Where< lobal

assi nment>

is:

=

Andis:

* *

Globalvariable

names

begin

and

end

with

the

*character.

?xisalocalvariable

x sag o a var a e.

E.g.

CLI PS> ( def gl obal ?*x* = 3

* * * *

CLI PS> ?*x*

3

CLI PS> ?*y*

4

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Examp e:

CLI PS> ( def r ul e ar ea

( r adi us ?r )

=>

( bi nd ?ar ea ( * ?*pi * ?*pi * ?r ) )

" " =

CLI PS> ( def f act s ar ea_ci r cl e ( r adi us 4) )

CLI PS> ( r eset )

CLI PS> ( r un)

Ar ea = 39. 47841751413609

Thevalueofadefglobalcanbechangedusingthebindcommand.

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rules:salienceandmodules.

Theuse

of

the

keyword

salience

allows

the

priority

of

rules

to

be

explicitly

.

Normallytheagendaactslikeastack.

themostrecentactivationplacedontheagendaisthefirsttofire.

,

regardlessof

when

the

rules

were

added.

Salienceissetusinganumericvaluerangingfromthesmallestvalueof

, , .

Ifarulehasnosalienceexplicitlyassignedbytheprogrammer,CLIPSassumesasalienceof0.

orlessersalienceandafterallruleswithgreatersalience.

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:

( def rul e f i r e- f i r st

( pr i or i t y f i r st )=>( pr i nt out t " Pr i nt f i r st " cr l f ) )

( def r ul e f i r e- second

( pr i or i t y second)=>( r i nt out t "Pr i nt second" cr l f ) )

( def rul e f i r e- t hi r d( pr i or i t y t hi r d)

=( pr i nt out t "Pr i nt t hi r d" cr l f ) )

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:

CLI PS> (unwatch al l )

CLI PS> ( r eset )LI PS> (assert (priority i r s t ) )

CLI PS> (assert (priority second) )

CLI PS> (assert (priority t hi r d) )CLI PS> ( r un)Pr i nt t hi r d

Pr i nt f i r stCLI PS>

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:

( def r ul e f i r e- f i r st

( decl ar e ( sal i ence 30) )pr i or i t y f i r st )

=>( pr i nt out t " Pr i nt f i r st " cr l f ) )

( def r ul e f i r e- second( decl ar e ( sal i ence 20) )( r i or i t second)=>( pr i nt out t "Pr i nt second" cr l f ) )

-( decl ar e ( sal i ence 10) )( pr i or i t y t hi r d)

( pr i nt out t "Pr i nt t hi r d" cr l f ) )SEEM 5750 25

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:

CLI PS> ( r eset )

CLI PS> ( asser t ( pr i or i t y second)pr i or i t y f i r st )

( pr i or i t y t hi r d) )CLI PS> ( agenda)30f i r e- f i r st : f - 220f i r e- second: f - 110f i r e- t hi r d: f - 3For a t ot al of 3 act i vat i ons.

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Forprogramsinvolvinghundredsorthousandsofrules,theintermixingof

maintenanceamajorproblem.

Asan

example,

consider

the

problem

of

performing

fault

detection,

isolation,andrecoveryofasystemsuchasanelectronicdevice.

DifferentPhasesforFaultDetection,Isolation,andRecoveryProblem

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Tousesaliencetoor anizetherules

Assignmentofsaliencefordifferentphases

controlknowledgeisstillbeingembeddedintotherulesusingsalience.

doesnotguaranteethecorrectorderofexecution.

controlknowledgefromthedomainknowledge,asshowninthefollowingfigure.

.

Control

rules

are

then

written

to

transfer

control

between

the

different

phases

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SeparationofExpertKnowledgefromControlKnowledge

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( def r ul e det ect i on- t o- i sol at i on( decl ar e ( sal i ence - 10) )

?phase ( r et r act ?phase)( asser t ( phase i sol at i on) ) )

u - - v y

( decl ar e ( sal i ence - 10) )?phase ( r et r act ?phase)( asser t ( phase r ecover y) ) )

( def r ul e r ecover y- t o- det ect i on( decl ar e ( sal i ence - 10) )?phase

( asser t ( phase det ect i on) ) )

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Eac o t eru esapp ica e oraparticu arp aseist engivenacontro

pattern.

( def r ul e f i nd- f aul t - l ocat i on- and- r ecover y( phase r ecover y)

( r ecover y- sol ut i on swi t ch- devi ce

?r epl acement on)

=>

( pr i nt out t "Swi t ch devi ce" ?r epl acement "on"

cr l f ) )

Asaliencehierarchy isadescriptionofthesaliencevaluesusedbyan

expertsystem.

membersareallgiventhesamesalience.

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W i et e act p ase etection isint e act ist,t e etectionto

isolationrulewillbeontheagenda.

Sinceit

has

alower

salience

than

the

detection

rules,

it

will

not

fire

until

all

of

thedetectionruleshavehadanopportunitytofire.

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FourLeve Sa ienceHierarc y

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Overuseofsalienceresultsinapoorlycodedprogram.

Amainadvantageofarulebasedprogramisthattheprogrammer

.

Salienceshouldprimarilybeusedasamechanismfor

determinin theorderinwhichrulesfire.

Salienceshould

not

be

used

as

amethod

for

selecting

asingle

rule

fromagroupofruleswhenpatternscanbeusedtoexpressthe

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