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Intro to Jess The Java Expert System Shell

Intro to Jess The Java Expert System Shell. By Jason Morris Morris Technical Solutions. Agenda. What are expert systems? What are rule-based expert systems? Introduction to Jess The Jess Language. Agenda. Scripting & The Jess API Demo 1 : Design Pattern Expert Demo 2 : Catalog Servlet

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Intro to Jess The Java Expert System Shell

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  1. Intro to Jess The Java Expert System Shell By Jason Morris Morris Technical Solutions

  2. Agenda • What are expert systems? • What are rule-based expert systems? • Introduction to Jess • The Jess Language

  3. Agenda • Scripting & The Jess API • Demo 1 : Design Pattern Expert • Demo 2 : Catalog Servlet • References and Further Study • Q & A

  4. Expert Systems… • Are a branch of artificial intelligence. • Simulate human reasoning in some domain. • “Reason” by heuristic or approximate methods. • Explain and justify solutions in user-friendly terms.

  5. Types Of Expert Systems • Case-Based Reasoning • Rule-Based Systems

  6. Rule-Based Expert Systems • Originated from AI research in the 70s and 80s. • Problem data stored as facts. • “Reason” using IF…THEN…ELSE rules. • Can “reason” deductively (forward-chaining) or inductively (backward-chaining).

  7. When to Use Rule-Based Systems • Problem Domain = narrow, well-understood domain theory • Knowledge Representation = facts and rules • Output = recommendation • Explanation = rule firing trace • Learning Ability = generally no (but…)

  8. Inference Process • Rules and facts compared using pattern matcher. • Matched rules activated into a conflict set. • Conflict set resolved into agenda (process called conflict resolution). • Rule engine fires on agenda. • Engine cycles until all rules are satisfied.

  9. The Java Expert System Shell • Developed at Sandia National Laboratories in late 1990s. • Created by Dr. Ernest J. Friedman-Hill. • Inspired by the AI production rule language CLIPS. • Fully developed Java API for creating rule-based expert systems.

  10. Rule-Based Expert System Architecture • Rule Base (knowledge base) • Working Memory (fact base) • Inference Engine (rule engine)

  11. Inference (Rule) Engines • Pattern Matcher – decides what rules to fire and when. • Agenda – schedules the order in which activated rules will fire. • Execution Engine – responsible for firing rules and executing other code.

  12. Inference Process • Match the facts against the rules. • Choose which rules to fire. • Execute the actions associated with the rules.

  13. How Does Jess Work? • Jess matches facts in the fact base to rules in the rule base. • The rules contain function calls that manipulate the fact base and/or other Java code. • Jess uses the Rete (ree-tee) algorithm to match patterns. • Rete network = an interconnected collection of nodes = working memory.

  14. Jess Architecture Diagram WORKING MEMORY INFERENCE ENGINE EXECUTION ENGINE PATTERN MATCHER RULE BASE AGENDA

  15. Procedural Programming • Traditional programming (BASIC, C, FORTRAN, Pascal, etc.). • Largely based on functions. • Programmer controls logic. • Sequential and deterministic. • Object-oriented programming is procedural within object methods.

  16. Declarative Programming • New programming paradigm - rules. • Programmer does not really control code logic. • Rule engine finds most efficient “path” of code execution. • Replaces (hard to maintain) nested IF…THEN…ELSE coding.

  17. What? I…I can’t control my code?? Well…yes and no…but don’t worry, Calvin! Wait a minute!

  18. Thought Experiment… • Imagine writing a procedural/OOP algorithm to solve a jigsaw puzzle. • 500+ pieces, different shapes and colors. • Polymorphism runs amok! Yet we manage to solve the puzzle…

  19. Intuition and Rules • Dump the puzzle pieces on a card table in no particular order. • Your brain instinctively begins to apply rules to solve the puzzle! • What might this look like in code?

  20. Intuitive Inferencing (corner_found (piece_is_corner) => (assert corner-found) (save_piece)) Your brain “knows” what to do with a corner piece … (edge_found (piece_is_edge) => (assert edge-found) (save_piece)) … and an edge piece.

  21. What’s Going On… • Your brain recalls rules or heuristics to solve the problem. • Your brain pattern-matches, prioritizes, and applies rules according to the facts in memory. • A particular solution algorithm emerges as rules “fire” on facts.

  22. The Jess Language • Architecturally inspired by CLIPS • LISP-like syntax. • Basic data structure is the list. • Can be used to script Java API. • Can be used to access JavaBeans. • Easy to learn and use.

  23. Obligatory Tradition (printout t “Hello World!” crlf) Your very first Jess program!

  24. Lists in Jess • (a b c) ; list of tokens • (1 2 3) ; list of integers • (+ 2 3) ; an expression • (“Hello world!”) ; a string • (foo ?x ?y) ; a function call Here are some valid lists in Jess:

  25. Jess Variables • Named containers that hold a single value. • Untyped. Begin with a ? mark. • Can change types during lifetime. • Assigned using bind function.

  26. Jess Variables and Lists Everything is a list in Jess! EXAMPLE: Adding two numbers (bind ?x 2) ; assign x = 2 (bind ?y 3) ; assign y = 3 (bind ?result (+ ?x ?y)) ; find sum

  27. foreach if/then/else while apply build eval progn Control Flow Common Jess-specific

  28. Jess Functions Even functions are lists. (deffunction get-input() “Get user input from console.” (bind ?s (read)) (return ?s))

  29. Jess Function Example (deffunction area-sphere (?radius) “Calculate the area of a sphere” (bind ?area (* (* (pi) 2)(* ?radius ?radius))) (return ?area))

  30. Jess Function Example How do we use this in Jess? (printout t "The surface area of a radius = 2 meter sphere is " + (area-sphere 2) + " m^2")

  31. Working With Facts • Facts have a head and one or more slots. • Slots hold data (can be typed). • Multislots can hold lists. • You can modify slot values at runtime. • Facts are constructed from templates.

  32. Jess Fact Types • Ordered – head only • Ordered – single slot. • Unordered – multiple slot, like a database record. • Shadow – slots correspond to properties of a JavaBean.

  33. Deftemplate Used to define the structure of a fact. • (deftemplate pattern • “A design pattern.” ;optional • (slot name) • (slot type (default “creation”)) • (slot intent) • (slot solution))

  34. Asserting Facts ;; Asserting a new “pattern” fact. (printout t “Enter pattern name:” crlf) (bind ?x getInput) (assert pattern (name ?x)) Facts store the initial conditions.

  35. All Kinds of Facts ;; An ordered fact with no slots – a placeholder that indicates state. (assert(answer-is-valid)) ;; A ordered fact of one slot (assert(weightfactor 0.75))

  36. Shadow Facts • defclass – creates a deftemplate from a bean. • definstance – adds bean to working memory. Shadow facts are unordered facts whose slots correspond to the properties of a JavaBean.

  37. Jess Rules… • … are the knowledge-base of the system. • … fire only once on a given set of facts. • … use pattern constraints to match facts. • … are much faster than IF-THEN statements.

  38. Rule Syntax • Rules have a “left-hand” side (LHS) and a “right-hand” side (RHS). • The LHS contains facts fitting certain patterns. • The RHS contains function calls.

  39. Simple Rule Example Checking working memory state. ;; A not very useful error handler (defrule report-error (error-is-present) => (printout t “There is an error” crlf))

  40. A More Complex Rule Using pattern bindings in rules. ;; A more useful error handler (defrule report-err ?err <- (is-error (msg ?msg)) => (printout t "Error was: " ?msg crlf) (retract ?err))

  41. More Pattern and Control Tools • Literal / variable constraints • Logical conditional tests • Predicate functions matching control and structure • Salience • Modules • Defquery • Backward-chaining

  42. Scripting Java from Jess • You can interactively access all Java APIs from Jess. • This makes exploring Java somewhat easier and immediate. • No code, compile, debug cycle.

  43. Scripting Java with Jess (import javax.swing.*) (import java.awt.*) (import java.awt.event.*) (set-reset-globals FALSE) (defglobal ?*frame* = (new JFrame "Hello PJUG")) (defglobal ?*button* = (new JButton "Click my PJUG")) (?*frame* setSize 500 300) ((?*frame* getContentPane) add ?*button*) (?*frame* setVisible TRUE)

  44. The Rete (ree-tee) Object • The reasoning engine and the central class in the Jess library. • Executes the built Rete network, and coordinates many other activities. • Rete is essentially a facade for the Jess API.

  45. Using the Jess API… try { Rete engine = new Rete(); engine.executeCommand( “printout t “Hello PJUG”); engine.run(); } catch (JessException je {} …is simple…all you really do need to do is call one or more Rete methods …

  46. Expert Systems References • Friedman-Hill, E. J., Jess In Action, Manning Press, 2003 • Jackson, P., Introduction to Expert Systems – 3rd Ed., Addison-Wesley, 1999 • Giarratano, J., Expert Systems: Principals and Programming, PSW-Kent, 1989

  47. Links • Download Jess at: http://herzberg.ca.sandia.gov/jess/index.shtml • Join the Jess user community at: http://herzberg.ca.sandia.gov/jess/mailing_list.shtml • See Dr. Friedman-Hill’s Jess in Action at: http://www.manning.com/friedman-hill/

  48. For Further Study • CLIPS Expert System Shell http://www.ghg.net/clips/CLIPS.html

  49. Q & A Thanks for your attention, and I hope that you try Jess!

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