Intro to CLIPS Paula Matuszek CSC 8750, Fall, 2004

1. Intro to CLIPSPaula MatuszekCSC 8750, Fall, 2004 Based on presentation from COMP474/6741 – Expert Systems Update: January 20, 2002Concordia University A. Andreevskaia and S. Mokhiv www.cs.concordia.ca/~comp474/tutorial/clips-intro.ppt Expert Systems, Paula Matuszek

2. CLIPS History • CLIPS = CLanguage Integrated Production System • Developed at NASA’s Johnson Space Center in the mid-1980-s • C was used as implementation language (because of restricted availability of LISP compilers and problems of integration LISP-code with non-LISP applications) • Initial version: a production rule interpreter. • Now: COOL = CLIPS Object-Oriented Language • Also JESS: Java Expert Systems Shell Expert Systems, Paula Matuszek

3. Where does it fit? • Classical Rule-Based Expert Systems • CLIPS as a Rule-Based Language • CLIPS’ Components • Forward Chaining (CLIPS) vs. Backward Chaining (e.g. MYCIN and derivatives) Expert Systems, Paula Matuszek

4. Why do we study CLIPS? • Advantages of CLIPS include: • A top-level interpreter • Production rule interpreter • Runs on many platforms (portability) like different flavors of UNIX, Linux, Windows, MacOS • A public-domain well-documented software • Fast • Easy to embed in other applications • Easy to get started Expert Systems, Paula Matuszek

5. Components of a Rule-Based Expert System Knowledge Base (RULES) Inference Engine Working Memory (FACTS) Agenda Explanation Facility Knowledge Acquisition Facility UI Expert Systems, Paula Matuszek

6. Versions of CLIPS • CLIPS is written in C => CLIPS is portable => there are different versions that run on different platforms: mac, unix, windows. • From CD you can get version for Windows • Latest version 6.20 can be downloaded from the CLIPS web site. Expert Systems, Paula Matuszek

7. Starting CLIPS 1. To start text-based CLIPS interpreter under UNIX you type clips and CLIPS> prompt will appear. You can try simple CLIPS commands. Remember - like LISP CLIPS requires all statements to be in ( ); otherwise, it will read them as simple string and just echo them. To exit CLIPS interpreter type (exit). Expert Systems, Paula Matuszek

8. Summary of Basic CLIPS Commands • (exit)to exit from CLIPS • (clear) to clear the environment from facts, rules, and other active definitions • (reset) to set the fact base to its initial state (clears existing facts; sets (initial-fact), and all (deffacts) constructs in the program). Perform (reset) before each program run! • (run) executes a program currently loaded into the CLIPS interpreter against currently defined rule- and fact-bases. Expert Systems, Paula Matuszek

9. More Basic CLIPS Commands • (load “filename.clp”) to load a CLIPS program into the interpreter from the file named filename.clp . This also does syntax check and makes constructs in the file defined. In some cases you may omit quotes in the name. • (facts) to display a list of currently active facts in the fact base. • (rules) to display a set of rules currently in the rule base. Expert Systems, Paula Matuszek

10. Comments in CLIPS • Program comments begin with a semicolon “;”. Everything after on the same line until the end of line is ignored.; This is an inline comment example • Construct comments – are used as a part of the CLIPS constructs (e.g. deftemplate, defrule, etc) and follows the construct’s name and enclosed in quotations.(defrule my-rule “my comment” (initial-fact) => (printout t “Hello” crlf)) Expert Systems, Paula Matuszek

11. Few Simple Clips Commands • To assert a fact: (assert (first-fact asserted)) • To define a rule: (defrule first_rule (first-fact asserted) => (assert (second-fact asserted))) Expert Systems, Paula Matuszek

12. “Hello World” in CLIPS (defrule start (initial-fact) => (printout t “Hello, world!” crlf)) Expert Systems, Paula Matuszek

13. To Make It Run • Type the code in a file, save it (e.g. hello-world.clp) • Start CLIPS (type clips or xclips) • Do: File -> Load (in XCLIPS) or type (load hello-world.clp) • When the file is loaded CLIPS will display: (load hello-world.clp) defining defrule start +j TRUE Expert Systems, Paula Matuszek

14. To Make It Run • Type (reset) • Type (run) Tip: You can also use the menu • To exit CLIPS use the menu, ^Q or (exit) Expert Systems, Paula Matuszek

15. Fields • There are seven data types (types of tokens) called fields in CLIPS. • float: [+\-] <digit>* [.<digit>*] [e|E[+|-]<digit>*] • integer: [+|-] <digits> * • symbol: [<] <char>* • string: “<char>* “ (e.g. “John”, “848-3000”) • external address • instance name • instance address Expert Systems, Paula Matuszek

16. Word • a word CANNOT start with these:< | & $ ? + - ( ) ; • a word CANNOT contain any of these:< | & ( ) ; Expert Systems, Paula Matuszek

17. Valid Expressions • Examples of valid words • fire • emergency-fire • activate_sprinkler_system • shut-down-electrical-junction-387 • !?#$^* • CLIPS is case-sensitive • So fireFIREFire are all different Expert Systems, Paula Matuszek

18. Valid Expressions • Examples of valid strings • “Activate the sprinkler system.” • “Shut down electrical junction 387.” • “!?#$^” • “<-;( ) +-” • Spaces act as delimiters to separate fields • These are different strings “fire” “fire “ “ fire” “ fire “ but would be the same with no quotes • Valid numbers • 1 1.5 .7 +3 -1 65 3.5e10 Expert Systems, Paula Matuszek

19. Facts • Fact is a chunk of information consisting of relation name, (optional) slots and slot values. Example:(person (name “John”)) • In CLIPS facts are frame structures often defined using the (deftemplate) construct. Expert Systems, Paula Matuszek

20. (deftemplate) (deftemplate <relation_name> [<comment>] <slot-definition>* ) <slot-definition> is: • (slot <slot-name>) • (field <slot-name>) • (multislot <slot-name>) Expert Systems, Paula Matuszek

21. Valid Facts • Examples of valid facts (single-field) (two fields) (speed 38 mph) (cost 78 dollars 23 cents) (name “John Doe”) Expert Systems, Paula Matuszek

22. (deftemplate) Example (deftemplate person “an example template” (multislot name) (slot age) (slot eye-color) (slot hair-color)) CLIPS> defining deftemplate: person TRUE Expert Systems, Paula Matuszek

23. Facts • Deftemplate can also be implicit = ordered facts: (numbers 1 2 3) • To add facts: (assert <fact>) (you can add more than one fact with the same (assert) command) • To remove facts: (retract <fact-index>*) • To list facts: (facts) will give facts’ identifiers like f-0 (not sequential) Expert Systems, Paula Matuszek

24. Facts Example CLIPS> (deftemplate course “electives” (slot number)) CLIPS> (assert (course (number comp674)) (course (number comp672))) <Fact-1> CLIPS> (facts) f-0 (course (number comp674)) f-1 (course (number comp672)) For a total of 2 facts CLIPS> (retract 1) CLIPS> (facts) f-0 (course (number comp674)) For a total of 1 fact Expert Systems, Paula Matuszek

25. Modifying Facts • To modify a fact: (modify <fact-index> <slot-modifier>*) <slot-modifier> is (<slot-name> <slot-value>) Example: CLIPS> (modify 0(number comp675)) <fact-2> CLIPS> (facts) f-2 (course (number comp675)) for a total of 1 fact Expert Systems, Paula Matuszek

26. Duplicating Facts • To create a duplicate of a fact: Example (continued) CLIPS> (duplicate 2 (number comp775)) <fact-3> CLIPS> (facts) f-2 (course (number comp675)) f-3 (course (number comp775)) For a total of 2 facts • Note: (duplicate) modifies a fact without deleting (retracting) the original, whereas (modify) does. Expert Systems, Paula Matuszek

27. Asserting a Group of Facts • To define groups of facts that represent the original (initial) knowledge: use (deffacts). Facts from (deffacts) are asserted using (reset) (or on (load)): (deffacts <deffacts-name> [<comment>] <facts>*) (reset) Expert Systems, Paula Matuszek

28. Retracting Facts • Facts can be removed or retracted using (retract <fact-index>) (retract 2) • Retract can be used for more than one fact (retract 1 2) Expert Systems, Paula Matuszek

29. (deftemplate) as a Record • Templates can be extended to hold more information like records:(deftemplate <deftemplate-name> [<optional comment>](slot <slot-name> (type <data-type>) [(default <value>)]) • Example: (deftemplate student “a student record”(slot name (type STRING))(slot age (type NUMBER) (default 18))) Expert Systems, Paula Matuszek

30. (deftemplate) Example • After the template declaration and adding: (deffacts student-Ids(student (name Tarzan))(student (name Jane) (age 19))) • The result is: (student (name Tarzan) (age 18))(student (name Jane) (age 19)) Expert Systems, Paula Matuszek

31. (deftemplate): Summary • Look at the templates as to user-defined types of facts. In a template you can have several slots (or fields), on which you can operate separately or all at the same time. Think of it as a sort of object. • This allows you to group multiple pieces of information of a given fact in one structure, which is described by the defftemplate construct, and the facts are instances of it. Expert Systems, Paula Matuszek

32. Rules (1) • LHS => RHS • Syntax: (defrule <rule-name> [<comment>] [<declaration>] ; salience <patterns>* ;LHS, premises, patterns, ;conditions, antecedent => <actions>*) ;RHS, actions, consequent Expert Systems, Paula Matuszek

33. Rules (2) • Example: (defrule class-A-fire-emergency (emergency fire)=> (printout t “FIRE!!!” crlf)) • Rules can have more than one pattern/premise:(defrule class-B-fire-emergency (emergency fire) (fire-class B)=> (printout t “Use carbon dioxide extinguisher” crlf)) Expert Systems, Paula Matuszek

34. Agenda • If the pattern(s) in the LHS of the rule match asserted facts, the rule is activated and put on the agenda. • Rules are ordered on the agenda according to their salience (read: priority). • When the agenda is empty the program stops. • Refraction: each rule is fired only once for a specific set of facts => use (refresh) Expert Systems, Paula Matuszek

35. Salience • Normally the agenda acts like a stack. • The most recent activation placed on the agenda is the first rule to fire. • Salience allows more important rules to stay at the top of the agenda regardless of when they were added. • If you do not explicitly say, CLIPS will assume the rule has a salience of 0. Expert Systems, Paula Matuszek

36. Conflict Resolution Strategies • Recency • Rules which use more recent data are preferred. • CLIPS time-tags WM elements • Specificity • Rules with more conditions are preferred to more general rules that are easier to satisfy. • Good if dealing with general rules with specific rules for exceptions • Refractoriness • A rule should not be allowed to fire more than once for the same data. • Prevents loops • Used in CLIPS (need (refresh) ) Expert Systems, Paula Matuszek

37. Conflict Resolution in CLIPS • First, CLIPS uses salience to sort the rules. Then it uses the other strategies to sort rules with equal salience. • CLIPS uses refraction, recency & specificity in the form of following 7 strategies: • The depth strategy • The breadth strategy • The simplicity strategy • The complexity strategy • The LEX strategy • The MEA strategy • It is possible also to set strategy to random • Syntax: (set-strategy <strategy>) Expert Systems, Paula Matuszek

38. Variables • Variable name is made of ? and one or more characters: • Example: (course (number ?cmp)) • Variables are used for • Pattern matching • I/O • As pointers to facts (fact indices) Expert Systems, Paula Matuszek

39. Variables Examples • (defrule grandfather (is-a-grandfather ?name)=> (assert (is-a-man ?name))) • (defrule grandfather (is-a-grandfather ?name) => (assert (is-a-father ?name)) (assert (is-a-man ?name)) (printout t ?name “ is a grandfather” crlf)) Expert Systems, Paula Matuszek

40. Fact Address • To remove a fact from the fact-list use (retract) • Before a fact can be retracted it must be specified to CLIPS by its index. • Rules can be used to modify the fact base. To achieve it variables have to be bound to fact addresses using ‘<-’:?num <- (course (number ?cmp)) • This appears in the LHS of the rule, and can be referred to in either LHS and RHS. Expert Systems, Paula Matuszek

41. Wildcards (1) To specify a general pattern we can use: • Single field variables: wildcard ? • Multifield variables: wildcard $? • (courses (numbers $?course_nums)) • (printout t “Your courses are” $?course_nums crlf)) • (list ? $? c ?) • can match these: (list a c e), (list a d c b) • but not these: (list c), (list c d), (list a c d b) Expert Systems, Paula Matuszek

42. Wildcards (2) • The fact (do carwash on Sunday) • will match any of the following • (do ? ? Sunday) • (do ? on ?) • (do ? on ?when) • (do $? ) • (do $? Sunday) • (do ?chore $?when) Expert Systems, Paula Matuszek

43. Retracting Facts Using Wildcards (defrule change-grandfather-fact ?old-fact <- (is-a-grandfather ?name) => (retract ?old-fact) (assert (has-a-grandchild ?name) (is-a-man ?name)) ) Expert Systems, Paula Matuszek

44. Retracting Facts Using Wildcards (2) • You can retract several facts:(retract ?fact1 ?fact2 ?fact3) • Or you can retract all of them at once:(retract *) Expert Systems, Paula Matuszek

45. Standard I/O • To print to STDOUT: (printout t …) • For the new line use: crlf • To read from STDIN into a field use:(read) Expert Systems, Paula Matuszek

46. Standard I/O Examples (1) • Keyboard input example: (defrule to-start “Rule to start & enter a name” (phase choose-name) => (printout t “Enter your name” crlf) (assert (your-name =(read)))) ; ’=’ is optional • Another example using a variable:(defrule to-start => (printout t “Enter something: ”) (bind ?something (read)) (printout t “You have entered ” ?something crlf)) Expert Systems, Paula Matuszek

47. Standard I/O Examples (2) • A slightly more advanced example:(defrule continue-check ?phase <- (phase check-continue)=> (retract ?phase) (printout t “Do you want to continue?” crlf) (bind ?answer (read))(if(or(eq ?answeryes)(eq ?answer y))then (assert (phase continue))else (halt))) Expert Systems, Paula Matuszek

48. File I/O • File I/O • (load <filename>) • (save <filename>) • NOTE: use \\ in paths if you trying to do it on Windows; or / will always work. Expert Systems, Paula Matuszek

49. To Display Constructs • To display constructs: (list-defrules) (list-deftemplates) (list-deffacts) • To display the text of definitions of the constructs: (ppdefrule <defrule-name>) (ppdeftemplate <deftemplate-name>) (ppdeffeacts <deffacts-name>) Expert Systems, Paula Matuszek

50. To Delete Constructs • To ”undefine“ a given construct: (undefrule <defrule-name>) (undeftemplate <deftemplate-name>) (undeffacts <deffacts-name>) Expert Systems, Paula Matuszek