Rules Assume cfile contains: And we issue the commands: (deffacts - - PowerPoint PPT Presentation

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Rules

Assume cfile contains: (deffacts initial-colors (colors red blue)) (defrule rule-1 (colors red white blue) => (assert (rule 1 fires)) ) (defrule rule-2 (colors red blue) => …) (defrule rule-3 (colors blue red) => …) (defrule rule-4 (colors red blue) => …) (defrule rule-4 (colors white red) => …)

And we issue the commands: clips> (load “cfile”) clips> (reset) clips> (facts) What is in the fact base? f-0 (initial-fact) f-1 (colors red blue) Suppose that we now: clips> (run) f-0 (initial-fact) f-1 (colors red blue) f-2 (rule 2 fired)

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Top Level Rule Commands

(watch <X>) -- where <X> is rules or activations (unwatch <X>) (rules) -- displays names of all rules in K.B. (ppdefrule <r-name>) -- display specified rule (matches <r-name>) -- display list of facts that match conditions of rule (set-break <r-name>) -- sets a break point on rule

• - system returns to top level

before execution of rule Covered Previously: New Commands:

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Top Level Rule Commands (cont.)

(remove-break <r-name>) -- removes break (remove-break) -- removes all breaks (show-breaks) -- display all break points (agenda) -- display all rule instantiations on agenda (run) -- start execution, running until no more rules can execute or (halt) is executed (run <n>) -- execute at most <n> rules

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Salience

• Numeric value associated with rule
• Range for value: -10000 to 10000
• Default value is 0
• Specifies the priority of rule execution
• Do not (over) use!

Conflict resolution: (1) Find rules which are satisfied (2) Pick rule with highest salience (3) If multiple rules, then apply conflict resolution to pick

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Example

(deffacts example-facts (a b c) (Test 1) ) (defrule r-1 (a b c) => (assert (rule 1 fires))) (defrule r-2 (declare (salience 1)) (Test 1) => . . .) (defrule r-3 (declare (salience 1)) (a b c) => ( . . .)

Which rule should be executed first? r-2 Then r-3 Then r-1

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Conflict Resolution Strategies

Newly activated rules are placed above all rules of same salience-stack based Suppose: fact-a activates rule-1 and rule-2 fact-b activates rule-3 and rule-4 fact-a is asserted before fact-b Then: rule-3 and rule-4 will be above rule-1 and rule-2 rule-3 and rule-4’s order will be arbitrary rule-1 and rule-2’s order will be arbitrary Depth Strategy

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Conflict Resolution Strategies (cont.)

Newly activated rules are placed below all rules of same salience-Queue based Suppose: fact-a activates rule-1 and rule-2 fact-b activates rule-3 and rule-4 fact-a is asserted before fact-b Then: rule-1 and rule-2 will be above rule-3 and rule-4 rule-3 and rule-4’s order will be arbitrary rule-1 and rule-2’s order will be arbitrary Breadth Strategy

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Newly activated rules of same salience are placed above all rules of equal or higher specificity Complexity Strategy Among rules of same salience, newly activated rules are placed below all activations with equal

• r lower specificity

Conflict Resolution Strategies (cont.)

Simplicity Strategy

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Conflict Resolution Strategies (cont.)

Each activation is assigned a random number This number determines the activations placement among others of same salience Random Strategy

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Conflict Resolution Strategies (cont.)

Scheme used in OPS-5 Rules are ordered by their salience An activation with a more recent fact-index is placed before rules with less recent fact indices If two activations have same recency, then one with higher specificity is placed first LEX Strategy

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Conflict Resolution Strategies (cont.)

Scheme available in OPS-5 Rules are ordered by their salience The recency of the fact associated with the first pattern is used to order If two activations have same fact-index for first pattern, then use the LEX strategy MEA Strategy

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Pattern Matching

• single field wildcard
• matches anything in corresponding

field of fact

• multi-field wildcard
• matches zero or more fields of a fact

? $?

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Pattern Matching (cont.)

?<var>

• single field variable
• <var> is some word
• this symbol matches anything in the

corresponding field of a fact

• value matched is bound to ?<var> for scope of

rule

• examples: ?cat ?color ?machine

$?<var>

• multi-field variable
• matches zero or more fields of a fact
• the value(s) of the matched fields is bound

to $?<var> for the scope of the rule

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Examples

LHS Condition Fact in Fact Base Match? (? ?) (data red) (data ?) (data red) (data ?) (data red green) (data ? ?) (data red green) (data red ?) (data red green) (data ? green) (data green) Yes Yes NO! Yes Yes NO! Single field wild cards

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Examples

LHS Condition Fact in Fact Base Match? ($?) (data red) (data $?) (data red) (data red $?) (data red) (data $?) (data red green) (data red green $?) (data red green) ($? green) (data red green) ($? red $?) (data red green) (data red $?) (data green red) (data $? red $?) (data green red) ($? $?) (data red) Yes Yes Yes Yes Yes Yes Yes NO! Yes Yes Multi-field wild cards

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Examples

LHS Condition Fact in Fact Base Match? (data red ?x) (data red green) (data red ?x) (data red “green”) (data red ?x) (data red 17.4) (data ?x ?x) (data red red) (data ?x ?x) (data red green) (data ?x ?y) (data red green) (data ?x ?y) (data red red) ?x=green ?x=“green” ?x=17.4 ?x=red NO! ?x=red ?y=green ?x=red ?y=red Single Field Variables

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Examples

LHS Condition Fact in Fact Base Match? (data red $?x) (data red) (data red $?x) (data red green) (data red $?x) (data red one two) (data $?x $?x) (data red red) (data $?x $?y) (data red green) $?x=() $?x=(green) $?x=(one two) $?x=(red) Multiple matches: Multi-Field Variables $?x=() $?y=(red green) $?x=(red) $?y=(green) $?x=(red green) $?y=()

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Fact Base: Rule Base: What rules will be instantiated?

Example of Rules with Variable Pattern Matching

(data red green) (data purple green) (defrule rule-1 (data red ?x) (data purple ?x) => . . .) (defrule rule-2 (data red $?x) (data purple $?x) => . . .) Both rule-1 and rule-2!

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Fact Base: Rule Base: What rules will be instantiated?

Example of Rules with Variable Pattern Matching

(data red green) (data red blue green) (data purple blue) (data purple blue brown) (defrule rule-1 (data red ?x) (data purple ?x) => . . .) (defrule rule-2 (data red $?x) (data purple $?x) => . . .) None!

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Fact Base: Rule Base: What rules will be instantiated?

Example of Rules with Variable Pattern Matching

(data red green) (data red blue green) (data purple blue) (data purple blue brown) (defrule rule-5 (data red ?x) (data purple ?y) => . . .) (defrule rule-6 (data red $?x) (data purple $?y) => . . .) One instantiation for rule-5, but 4 for rule-6!

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Constraints can be placed on the fields of a condition using logical operators: Syntax:

Field Constraints

& and | or ~ not <val1> & <val2> <val1> | <val2> ~<val> ?<var> & (<val1> | <val2>) ?<var> & ~<val>

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Examples

Condition Match Facts (data ~red) (data red) (data ~red&~blue) (data green) (data red|blue) (data red) (data ?col&~red) (data green) (data ?col&~red&~blue) (data red) (data ?col&red|blue) (data red) NO Yes Yes ?col=green NO ?col=red

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Sample Rule

(defrule complex-eye-hair-match (person ?name1 ?eyes1&blue|green ?hair1&~black) (person ?name2&~?name1 ?eyes2&~?eyes1 ?hair2&red|?hair1) => (printout t ?name1 “ has ” ?eyes1 “ eyes and ” ?hair1 “ hair” crlf) (printout t ?name2 “ has ” ?eyes2 “ eyes and ” ?hair2 “ hair” crlf) )

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Built-in Functions

+ - * / ** != = < <= > >= eq neq numberp stringp wordp evenp

• ddp

integerp Arithmetic: Relational: Predicate:

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Examples

Rule Facts Instantiated?

(defrule r-1 (data ?Y) (data 3) (data ?X &:(> ?X ?Y) ) (data 5) => . . . ) (defrule r-2 (data1 ?Y) (data2 4) (data2 ?X &:(= ?X ?Y)) (data1 4) => . . . )

(data ?X &: (numberp ?X) ) (data ?X &: (numberp ?X) & ~: (oddp ?X) ) (data ?X &: (numberp ?X) |: (wordp ?X) )

?X = 5 ?Y = 3 ?Y = 4 ?X = 4

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Examples (cont.)

Rule Facts Instantiated?

(defrule r-3 (data1 ?Y) (data1 red) (data2 ?X &:(= ?X ?Y) ) (data2 4) => . . . ) (defrule r-4 (data1 ?Y) (data1 red) (data2 ?X &:(eq ?X ?Y)) (data2 4) => . . . ) (defrule r-5 (data1 ?Y) (data2 4) (data2 ?X &:(neq ?X ?Y)) (data1 red) => . . . ) ERROR! NO! ?Y = red ?X = 4

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I/O Functions

• Allows input of a single field

(read <logical-name>)

• Encountering end-of-file returns EOF
• Example:

(defrule rule-1 (initial-fact) => (bind ?input (read)) (assert (data ?input)) )

Read

• Alternative:

(defrule rule-1 (initial-fact) => (assert (data =(read t))) )

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I/O Functions (cont.)

• Similar to read
• Input is an entire line
• Returns line as a string

(readline <logical-name>) Readline

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Open and Close

Files must be opened before used for I/O and closed when finished Modes: R read acess only (default) W write access only R+ read and write access A append access only Close with no arguments closes all opened files (open “<file-name>“ <logical-name> “<mode>“) (close <logical-name>)

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Open and Close (cont.)

Example: (defrule read-from-file (initial-fact) => (open “data.clp” my-data) (assert (data1 =(readline mydata))) (close) )