Preliminary Introduction to JESS

1. Preliminary Introduction to JESS Mostly adopted from Jason Morris notes (Morris Technical Solutions)

2. 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.

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

4. 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.

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

6. 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 Retealgorithm to match patterns. • Rete network = an interconnected collection of nodes = working memory.

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

8. 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.

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

10. 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:

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

12. 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

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

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

15. 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")

16. 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.

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

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

19. 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.

20. 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))

21. 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.

22. 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.

23. 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.

24. 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))

25. 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))

26. Scripting Java from Jess • You can interactively access all Java APIs from Jess. • This makes exploring Java somewhat easier and immediate.

27. 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)

28. The Jess API • jess - inference engine “guts”. • jess.awt – GUI wrappers. • jess.factory - Allows extensions that “get into the guts of Jess”. Organized into 3 packages, 64 classes (not hard to learn)

29. The ReteObject • 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.

30. Using the Jess API… try { Rete engine = new Rete(); engine.executeCommand(“printout t “Hello CS437”); engine.run(); } catch (JessException je {} It is simple. All you really need to do is to make an instance of Rete and call one or more Rete methods.

31. 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/ • CLIPS Expert System Shell http://www.ghg.net/clips/CLIPS.html • FuzzyJ Website http://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.html