1. JESS : Java Expert System Shell
Mark Maslyn

2. Java Expert System Shell
Java Application
A “Rules-Engine”
Developed by Ernest Friedman-Hill at Sandia National Laboratory
Processes “Jess” Scripting Language
Can by called by Java Programs or act as a Java Command Interpreter

3. Java and JESS
Jess Calls Java
JESS
Java Calls Jess
Java App

4. JESS Uses Templates (data structure definitions)
Facts (templates with data values)
Rules (logic and program flow)
Commands (to the JESS shell)
Java Beans

5. "Hello World" in JESS c:\>java jess.Main
Jess, the Java Expert System Shell
Copyright (C) 2001 E.J. Friedman Hill and the Sandia Corporation
Jess Version 6.1p7 5/7/2004
Jess>(printout t "Hello World" crlf)
Hello World
Jess>

6. Jess Can Call Java Functions
(bind ?frame (new JFrame “Pumps Demo”))
(call (?frame getContentPane)
setLayout(new GridLayout 2 3))

7. Java Calling JESS import jess.*; ... Rete engine = new Rete( );
engine.executeCommand (
“(printout t \”Hello Word\” crlf)”);

8. Jess Value Types RU.FLOAT RU.INTEGER RU.LONG RU.LIST RU.STRING
float, double
long, short, int, byte, char
Same
A Java array
String, char, Character
Wrapper classes

9. Returning Values import jess.*; ... Rete engine = new Rete( );
Value result = engine.executeCommand (
“(+ 2 2 )”);
System.out.println(result.intValue(null));

10. Steps to Solve A Problem With Jess
Define Templates and Facts
Write Rules
Run Jess

11. Templates (Data Structures)
(deftemplate employee
“employees in the database”
(slot name)
(slot gender)
(slot job_title))

12. Facts (Structures with Values
(employee (name John Smith)
(gender male)
(job_title programmer))

13. defrule example_rule LHS => RHS
Rule Syntax:
if (LHS) then RHS
defrule example_rule LHS => RHS
if (left hand side) conditions are true
then clauses on the right hand side are executed

14. Example Rule “if” (LHS) rule name “then” (RHS)
(defrule change-baby-if-wet
?wet <- (baby-is-wet)
=> (change-baby)
(retract ?wet))
“then” (RHS)

15. Rule Conditions Can’t Call FunctionsNO
(defrule equals
(eq 1 1) =>
(printout t “1 and 1 are equal” crlf))
YES
(defrule equals
(test (eq 1 1) ) =>
(printout t “1 and 1 are equal” crlf))

16. Search Space Problems
Jess Can Solve Constraint or Search Space Problems (e.g. Logic, Scheduling)

17. 4 Golfers Logic Problem
Four Golfers: Fred, Joe, Bob and Tom are in line at the tee
Golfer to Fred's right is wearing blue pants
Joe is second in line
Bob is wearing plaid pants
Tom isn't in position 1 or 4
Tom is wearing orange pants

18. Step 1: Define Templates
(deftemplate pants-color
(slot person)
(slot color))
(deftemplate golfer-position
(slot person)
(slot position))
(pants-color (person Bob) (color red))
(golfer-position (person Bob) (position 2))

19. Step 2: Write JESS rules to generate combinations as “facts”
(defrule generate-combos
=>
(foreach ?name (create$ Fred Joe Bob Tom)
(foreach ?color (create$ red blue plaid orange)
(assert (pants-color (person ?name)
(color ?color))))
(foreach ?golfer-position (create$ )
(assert (golfer-position (person ?name)
(position ?pos))))))

20. Step 3: Run JESS to find solution.
(defrule find-solution
;; The golfer to Fred's right is wearing blue pants.
(position (person Fred) (position ?p1))
(pants-color (person Fred) (color ?c1))
...
=>
(printout t Fred " " ?p1 " " ?c1 crlf)
(printout t Joe " " ?p2 " " ?c2 crlf)
(printout t Bob " " ?p3 " " ?c3 crlf)
(printout t Tom " " ?p4 " " ?c4 crlf) )

21. Logic Problem Demo

22. Search Tree

23. Rules Engine
Jess Can Act As a “Rules Engine” For Expert System Type Problems (e.g. Diagnosis, Configuration, Personalization)

24. Rule Engines Contain
Rule base
Working memory
Inference engine

25. Asimov's 3 Laws of Robotics
1) A robot may not injure a human being or, through inaction allow a human being to come to harm.
2) A robot must obey orders given it by human beings except where such orders would conflict with the First Law.

26. 3 Laws (Continued)
3) A robot must protect its own existence as long as such protection does not conflict with the First or Second Laws.

27. Robots Existence Rule (defrule third_law (first_law_obeyed)
(second_law_obeyed)
=> protect_robots_existence)

28. Animals Expert System Demo

29. “Shadow” Facts and Java Beans
JESS fact
Java Bean
(employee
(name “John Smith”)
(gender Male)
(job_title programmer))

30. Shadow Facts Java Bean public class dimmerSwitch {
private int brightness = 0;
public int getBrightness( )
{ return brightness; }
public void setBrightness( int value )
{ brightness = value; } }

31. Adding the Java Bean to Jess...
Step 1: Generate a Jess template with defclass
(defclass dimmer dimmerSwitch)
Step 2: Create and bind an instance of this class in Jess
(bind ?ds (new dimmerSwitch))
(definstance dimmer ?ds)

32. Calling the Java Bean... Step 3: Call the Java Bean methods
(call ?ds setBrightness 10 ))

33. Customization and Filtering
Customer in DB?
Customer Name, Address
Java App DB
Packages
Credit Score
Promos
JESS
Web Service
Rules
Filtered Results

34. Lookup Customer and Credit Score
Customer in DB?
Customer Name, Address
Java App DB
Packages
Credit Score
JESS
Promos
Web Service
Rules
Filtered Results

35. Load Packages, Promotions and Rules
Customer in DB?
Customer Name, Address
Java App DB
Packages
Credit Score
Promos
JESS
Web Service
Rules
Filtered Results

36. Example Packages by Partner
Price
Description
SBC
Free-For-All
49.95
TV with no equipment to buy!
Digital Home Advantage
29.95 
Connect up to 2 TV's free!
Sprint
America's Top 60
34.95
America's Top 60 Cable Channels!
59.95
America's Top 100
America's Top 100 Cable Channels!
Qwest
39.95

37. Packages and Promotions Templates
deftemplate package (slot partner)
(slot name)
(slot desc)
(slot price))
deftemplate promotion (slot partner)
(slot name)
(slot desc)
(slot amount))

38. Retrieve Packages By Partner Rule
(assert (package-partner Sprint)) ;; example partner name …
;; find all packages with Sprint as the partner
(defrule get-packages
(prod-partner ?p)
(package (partner ?p)(name ?n) (desc ?d) (price ?pr))
=>
(assert (results ?p ?n ?d ?pr)))

39. Filter Packages By Credit Score Rule
(assert (credit-score 620)) …
(defrule filter-by-credit-score
(credit-score ?c)
?f<-(results (partner ?p)(name ?n)(desc ?d) (price ?pr))
(test (and (< ?c 650)(> ?pr 39.95)))
=>
(retract ?f))

40. Use Rules to Filter Packages and Promotions
Customer in DB?
Customer Name, Address
Java App DB
Packages
Credit Score
JESS
Promos
Web Service
Rules
Filtered Results

41. JESS Pros and Cons Pros Very Flexible System
Free for Government or Academic Use
Source Code Available
Very Fast Rete Algorithm
Planned Integration with Eclipse
Cons
Lisp – like syntax
Limited GUI interface – New Interface in 7.0

42. Jess Resources Jess Home Page herzberg.ca.sandia.gov/jess/index.shtml
Jess In Action (Book)
My Website
(click on the Jess link)