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Expert Systems

Expert Systems. Chapter 7 Introduction to CLIPS. 7.5. Entering and Exiting CLIPS. A> CLIPS  CLIPS (V6.5 09/01/97) CLIPS> exit exit CLIPS> (+ 3 4)  7 CLIPS> (exit) A>. 7.6. Facts. A “chunk” of information in CLIPS is called a fact .

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Expert Systems

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  1. Expert Systems Chapter 7 Introduction to CLIPS

  2. 7.5 Entering and Exiting CLIPS • A> CLIPS  CLIPS (V6.5 09/01/97)CLIPS> exitexitCLIPS> (+ 3 4) 7CLIPS> (exit)A>

  3. 7.6 Facts • A “chunk” of information in CLIPS is called a fact. • Facts consists of a relation name followed by zero or more slots and their associated values. (person (name “John Q. Public”) (age 23) (eye-color blue) (hair-color black)) The order in which slots are specified is irrelevant.

  4. Deftemplate Construct • Defining the list of valid slots for a given relation name. • Analogous to a record structure in Pascal. • Format: (deftemplate <relation-name> [<optional-comment>] <slot-definition>*) <slot-definition> : (slot <slot-name> | ( multislot <slot-name>)

  5. Defining “person” fact (deftemplate person “An example deftemplate” (slot name) (slot age) (slot eye-color) (slot hair-color)) The “person” template (person (name “John Q. Public”) (age 23) (eye-color blue) (hair-color black)) The fact following the format of “person” template

  6. Multifield Slots • Slots of a fact that have been specified with the slot keyword in their deftemplates are allowed to contain only one value. • Which specified with multislot keyword are allowed to contain zero or more values.

  7. Defining “person” factwith multislot (deftemplate person “An example deftemplate” (multislot name) (slot age) (slot eye-color) (slot hair-color)) Specifying multislot (person (name John Q. Public) (age 23) (eye-color blue) (hair-color brown)) Multislot

  8. Ordered Facts • Facts with a relation name that has a corresponding deftemplate are called deftemplate facts. • Facts with a relation name that does not have a corresponding deftemplate are called ordered facts. • Whenever CLIPS encounters an ordered fact it automatically creates an implied deftemplate for that fact (as opposed to an explicit deftemplate, created using the deftemplate construct).

  9. Example:(number-list 7 9 3 4 20)is equivalent to defining(deftemplate number-list (multislot values))and then defining the fact as(number-list (values 7 9 3 4 20))

  10. Cases where Ordered Facts are useful • Case 1: Facts consisting of just a relation name are useful as flags and look identical regardless of whether a deftemplate has been defined.(all-orders-processed) • Case 2: For facts containing a single slot, the slot name is usually synonymous with the relation name.(time (value 8:45))can be changed to(time 8:45)

  11. CONSTRUCT Is-a DEFTEMPLATE IS-A Is-a IMPLIED DEFTEMPLATE EXPLICIT DEFTEMPLATE FACT Creates Is-a Creates Is-a Is-a ORDERED FACT DEFTEMPLATE FACT (deftemplate person (multislot name) (slot age) (slot eye-color) (slot hair-color)) Is-a Is-a (number-list 7 9 3 4 20) (person (name John Q. Public) (age 23) (eye-color blue) (hair-color brown))

  12. CONSTRUCT Is-a DEFTEMPLATE IS-A Is-a IMPLIED DEFTEMPLATE EXPLICIT DEFTEMPLATE FACT Creates Is-a Creates Is-a Is-a ORDERED FACT DEFTEMPLATE FACT (deftemplate person (multislot name) (slot age) (slot eye-color) (slot hair-color)) Is-a Is-a (number-list 7 9 3 4 20) (person (name John Q. Public) (age 23) (eye-color blue) (hair-color brown)) Relation Name

  13. CONSTRUCT Is-a DEFTEMPLATE IS-A Is-a IMPLIED DEFTEMPLATE EXPLICIT DEFTEMPLATE FACT Creates Is-a Creates Is-a Is-a ORDERED FACT DEFTEMPLATE FACT (deftemplate person (multislot name) (slot age) (slot eye-color) (slot hair-color)) Is-a Is-a (number-list 7 9 3 4 20) (person (name John Q. Public) (age 23) (eye-color blue) (hair-color brown)) Fields

  14. CONSTRUCT Is-a DEFTEMPLATE IS-A Is-a IMPLIED DEFTEMPLATE EXPLICIT DEFTEMPLATE FACT Creates Is-a Creates Is-a Is-a ORDERED FACT DEFTEMPLATE FACT Slot Name (deftemplate person (multislot name) (slot age) (slot eye-color) (slot hair-color)) Is-a Is-a (number-list 7 9 3 4 20) (person (name John Q. Public) (age 23) (eye-color blue) (hair-color brown)) Slots Slot Value (a field)

  15. CONSTRUCT Is-a DEFTEMPLATE IS-A Is-a IMPLIED DEFTEMPLATE EXPLICIT DEFTEMPLATE FACT Creates Is-a Creates Is-a Is-a ORDERED FACT DEFTEMPLATE FACT (deftemplate person (multislot name) (slot age) (slot eye-color) (slot hair-color)) Is-a Is-a (number-list 7 9 3 4 20) (person (name John Q. Public) (age 23) (eye-color blue) (hair-color brown)) Multifield Slot Single-field Slot

  16. 7.7 Adding Facts • Syntax:(assert <facts>+) • Example: CLIPS>(deftemplate person (slot name) (slot age) (slot eye-color) (slot hair-color)) CLIPS>(assert (person (name “John Q. Public”) (age 23) (eye-color blue) (hair-color black))) <Fact-0>CLIPS>

  17. Display the facts • Syntax: (facts) • Example:CLIPS> (facts) f-0 (person (name “John Q. Public”) (age 23) (eye-color blue) (hair-color black))For a total of 1 fact.CLIPS> Fact identifier, 0: fact index

  18. Asserting multiple facts withsingle assert (assert (person (name “John Q. Public”) (age 23) (eye-color blue) (hair-color black)) (person (name “Jane Q. Public”) (age 26) (eye-color green) (hair-color red)))

  19. Removing Facts • Syntax: (retract <fact-index>+) • Example: John Q. Public can be removed from the fact list with the command(retract 0)and Jane can be removed by(retract 1) • Attempting to retract a nonexistent fact will produce an error.

  20. 7.8 Modifying Facts • Syntax: (modify <fact-index> <slot-modifier>+) • Example:CLIPS> (modify 0 (age 24))<Fact-2>CLIPS> (facts) f-2 (person (name “John Q. Public”) (age 24) (eye-color blue) (hair-color black))For a total of 1 fact.CLIPS> A new fact index is generated for a modified fact.

  21. Duplicating Facts • Works the same with modify but not retracting the original fact. • Syntax: (duplicate <fact-index> <slot-modifier>+)

  22. Example:CLIPS> (duplicate 2 (name “Jack S. Public”))<Fact-3>CLIPS> (facts) f-2 (person (name “John Q. Public”) (age 24) (eye-color blue) (hair-color black))f-3 (person (name “Jack S. Public”) (age 24) (eye-color blue) (hair-color black))For a total of 2 facts.CLIPS>

  23. 7.9 Debugging • Syntax: (watch <watch-item>) • The <watch-item> is one of the symbols facts, rules, activations, statistics, compilations, focus, or all. • By default, when CLIPS is first started, compilations are watched and the remaining watch items are not watched.

  24. Indicating that the fact is being retracted. • Example:CLIPS> (facts 3 3)f-3 (person (name “Jack S. Public”) (age 24) (eye-color blue) (hair-color black))For a total of 1 fact.CLIPS> (watch facts) CLIPS> (modify 3 (age 25)) <== f-3 (person (name “Jack S. Public”) (age 24) (eye-color blue) (hair-color black))==> f-4 (person (name “Jack S. Public”) (age 25) (eye-color blue) (hair-color black))<Fact-4>CLIPS> Indicating that the fact is being asserted.

  25. 7.10 Defining Initial Knowledge • It is convenient to be able to automatically assert a set of facts instead of typing in the same assertions from the top level. • Initial knowledge: facts that are known to be true before running a program. • Groups of facts that represent initial knowledge can be defined using the deffacts construct.

  26. Deffacts Construct • Syntax: (deffacts <deffacts name> [<optional comment>] <facts>*) • Example: (deffacts people “Some people we know” (person (name “John Q. Public”) (age 24) (eye-color blue) (hair-color black)) (person (name “Jack S. Public”) (age 24) (eye-color blue) (hair-color black)) (person (name “Jane Q. Public) (age 36) (eye-color green) (hair-color red)))

  27. Reset • The reset command removes all facts from the fact list and then asserts the facts from existing deffacts statement. CLIPS> (unwatch facts) CLIPS> (reset)  CLIPS> (facts)  f-0 (initial-fact) f-1 (person (name “John Q. Public”) (age 24) (eye-color blue) (hair-color black))f-2 (person (name “Jack S. Public”) (age 24) (eye-color blue) (hair-color black)) f-3 (person (name “Jane Q. Public) (age 36) (eye-color green) (hair-color red)) For a total of 4 facts. CLIPS>

  28. Initial Fact • A new fact generated by the reset command called initial-fact. • Upon startup, CLIPS automatically defines the following two constructs:(deftemplate initial-fact) (deffacts initial-fact (initial-fact)) • Even if no any deffacts statements defined, a reset will assert the fact (initial-fact).

  29. 7.11 Rules • Rules can be typed directly into CLIPS or loaded in from a file of rules created by an editor. • Example: pseudocode of plant monitoringIF the emergency is a fire THEN the response is to activate the sprinkler system • Representing emergency: (deftemplate emergency (slot type)) • Representing response: (deftemplate response (slot action))

  30. Rule Representation • General format of a rule:(defrule <rule name> [<comment>] <patterns>* ;Left-hand side (LHS) => <actions>*) ;Right-hand side (RHS) • Representing the rule: (defrule fire-emergency “An example rule” (emergency (type fire)) => (assert (response (action activate-sprinkler-system))))

  31. Conditional Elements • After the rule header are zero or more conditional elements (CEs). • The simplest type of CE is a pattern CE or simply pattern. • Each pattern consists of one or more constraints intended to match the fields of a deftemplate fact.

  32. pattern Conditional Elements pattern Example (defrule fire-emergency “An example rule” (emergency (type fire)) (emergency (type flood)) => (assert (response (action activate-sprinkler-system))))

  33. Rule without Pattern • If a rule has no patterns, the special pattern (initial-fact) will be added as a pattern for the rule. • Since the initial-fact deffacts is automatically defined, any rules with no patterns on their LHSs will be activated when a reset command is performed since the (initial-fact) fact will automatically be asserted. • Thus any rule without LHS patterns will be placed on the agenda when a reset is performed

  34. 7.12 Program Execution • Syntax: (run [<limit>]) limit: maximum number of rules to be fired • The facts asserted by a reset satisfy the patterns of one or more rules and place activations of these rules on the agenda. • Issuing the run command then begins execution of the program.

  35. Displaying the Agenda • Syntax: (agenda) • Example: CLIPS> (reset) CLIPS> (assert (emergency (type fire)))<Fact-1> CLIPS> (agenda)0 fire-emergency: f-1For a total of 1 activation.CLIPS>

  36. Run • (Example continue)CLIPS> (run)CLIPS> (facts)f-0 (initial-fact)f-1 (emergency (type fire))f-2 (response action activate-sprinkler-system))For a total of 3 facts.CLIPS>

  37. Refraction • Refraction: Rules in CLIPS won’t fire more than once for a specific set of facts. • Without refraction, expert systems would always be caught in trivial loops. • If necessary, the rule can be made to fire again by retracting the fact(emergency (type fire))and asserting it again.

  38. Refresh Command • Used to make the rule fire again. • Syntax: (refresh <rule-name>) • Example:CLIPS> (agenda)CLIPS> (refresh fire-emergency) CLIPS> (agenda) 0 fire-emergency: f-1For a total of 1 activation.CLIPS>

  39. Watching Activations • Example:CLIPS> (reset) CLIPS> (watch activations) CLIPS> (assert (emergency (type fire))) ==> Activation 0 fire-emergency: f-1<Fact-1>CLIPS> (agenda) 0 fire-emergency: f-1For a total of 1 activation.CLIPS> (retract 1) <== Activation 0 fire-emergency: f-1CLIPS> (agenda) CLIPS>

  40. Watching Rules • CLIPS will print a message whenever a rule is fired. • Example:CLIPS> (reset) CLIPS> (watch rules) CLIPS> (assert (emergency (type fire))) ==> Activation 0 fire-emergency: f-1<Fact-1>CLIPS> (run) FIRE 1 fire-emergency: f-1CLIPS> (agenda) CLIPS>

  41. Displaying Construct List • Example:CLIPS> (list-defrules) fire-emergencyFor a total of 1 rule.CLIPS> (list-deftemplates) initial-factemergencyresponseFor a total of 3 deftemplates.CLIPS> (list-deffacts) initial-factFor a total of 1 deffacts.CLIPS>

  42. Pretty Print • Example:CLIPS> (ppdefrule fire-emergency) (defrule MAIN::fire-emergency “An example rule” (emergency (type fire)) => (assert (response (action activate-sprinkler-system))))CLIPS> (ppdeftemplate response) (deftemplate MAIN::response (slot action))CLIPS> (ppdeffacts initial-fact) CLIPS> (deffacts start-fact (start-fact)) CLIPS> (ppdeffacts start-fact) (deffacts MAIN::start-fact (start-fact))CLIPS>

  43. Deleting Constructs • Example:CLIPS> (undeffacts start-fact) CLIPS> (list-deffacts) initial-factFor a total of 1 deffacts.CLIPS> (undefrule fire-emergency) CLIPS> (list-defrules) CLIPS>

  44. Clearing all Constructs • Syntax: (clear) • Example:CLIPS> (list-deffacts) CLIPS> (list-deftemplates) emergencyresponsestart-factFor a total of 3 deftemplates.CLIPS> (clear)CLIPS> (list-deffacts) initial-factFor a total of 1 deffacts.CLIPS> (list-deftemplates) initial-factFor a total of 1 deftemplate.CLIPS> After clearing, it adds the initial-facts deffacts to the environment.

  45. Printout • Syntax: (printout <logical-name> <print-items> *) • Example:(defrule fire-emergency (emergency (type fire)) => (printout t “Activate the sprinkler system” crlf)) • Output:“Activate the sprinkler system” Stands for the standard output device of terminal. Carriage return/Line feed

  46. 7.15 Multiple Rules (defrule fire-emergency (emergency (type fire)) => (printout t “Activate the sprinkler system” crlf))(defrule flood-emergency (emergency (type flood)) => (printout t “Shut down electrical equipment” crlf))

  47. Rules with Multiple Patterns (deftemplate extinguisher-system (slot type) (slot status))(defrule class-A-fire-emergency (emergency (type class-A-fire)) (extinguisher-system (type water-sprinkler) (status off)) => (printout t “Activate water sprinkler” crlf))(defrule class-B-fire-emergency (emergency (type class-B-fire)) (extinguisher-system (type carbon-dioxide) (status off)) => (printout t “Use carbon dioxide extinguisher” crlf))

  48. 7.17 Loading Constructs • Syntax: (load <file-name>) • Example:CLIPS> (load “fire.clp”) Defining deftemplate: emergencyDefining deftemplate: responseDefining defrule: fire-emergency +jTRUECLIPS> • If compilations are not being watched, then the character *, %, and $ will be used for defrules, deftemplates, and deffacts.

  49. Saving Constructs • Syntax: (save <file-name>) • Example:(save “B:fire.clp”)

  50. Comments ;* Programmer: G. D. Riley ; Deftemplates here (deftemplate emergency (slot type)) ; ;The purpose of this rule is to activate ; the sprinkler system if there is a fire (defrule fire-emergency ; There is a fire emergency (emergency (type fire)) => ; Activate the sprinkler system (printout t “Activate the sprinkler system” crlf))

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