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Intro to Jess The Java Expert System Shell. By Jason Morris Morris Technical Solutions. Quotable Quotes. Each problem that I solved became a rule which served afterwards to solve other problems. - Rene Descartes. Quotable Quotes .

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Intro to Jess The Java Expert System Shell

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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

quotable quotes
Quotable Quotes

Each problem that I solved became a rule which served afterwards to solve other problems.- Rene Descartes

quotable quotes3
Quotable Quotes

As a rule we disbelieve all the facts and theories for which we have no use.

- William James

quotable quotes4
Quotable Quotes

Hell, there are no rules here -- we're trying to accomplish something.

- Thomas A. Edison

quotable quotes5
Quotable Quotes

Get your facts first, and then you can distort them as much as you please.

- Mark Twain

quotable quotes6
Quotable Quotes

If the facts don't fit the theory, change the facts.- Albert Einstein

quotable quotes7
Quotable Quotes

There are two rules for success:

1) Never tell everything you know.

- Roger H. Lincoln

quotable quotes8
Quotable Quotes

Facts do not cease to exist just because they are ignored.

- Aldous Huxley

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

5 minute break

  • Scripting & The Jess API
  • Demo 1 : Design Pattern Expert
  • Demo 2 : Catalog Servlet
  • References and Further Study
  • Q & A
expert systems
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.
types of expert systems
Types Of Expert Systems
  • Neural Networks
  • Blackboard Systems
  • Belief (Bayesian) Networks
  • Case-Based Reasoning
  • Rule-Based Systems
rule based expert systems
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).
when to use rule based systems
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…)
inference process
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.
the java expert system shell
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.
rule based expert system architecture
Rule-Based Expert System Architecture
  • Rule Base (knowledge base)
  • Working Memory (fact base)
  • Inference Engine (rule engine)
inference rule engines
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.
inference process19
Inference Process
  • Match the facts against the rules.
  • Choose which rules to fire.
  • Execute the actions associated with the rules.
how does jess work
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.
jess architecture diagram
Jess Architecture Diagram












procedural programming
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.
declarative programming
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.
wait a minute

What? I…I can’t control my code??

Well…yes and no…but don’t worry, Calvin!

Wait a minute!
thought experiment
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…

intuition and rules
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?
intuitive inferencing
Intuitive Inferencing




(assert corner-found)


Your brain “knows” what to do with a corner piece …




(assert edge-found)


… and an edge piece.

what s going on
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.
the jess language
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.
obligatory tradition
Obligatory Tradition

(printout t “Hello PJUG-ers!” crlf)

Your very first Jess program!

lists in jess
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:

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

control flow







Control Flow



jess functions
Jess Functions

Even functions are lists.

(deffunction get-input()

“Get user input from console.”

(bind ?s (read))

(return ?s))

jess function example
Jess Function Example

(deffunction area-sphere (?radius)

“Calculate the area of a sphere”

(bind ?area (* (* (pi) 2)(* ?radius ?radius)))

(return ?area))

jess function example37
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")

working with facts
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.
jess fact types
Jess Fact Types
  • Ordered – head only.
  • Ordered – single slot.
  • Unordered – multiple slot, like a database record.
  • Shadow – slots correspond to properties of a JavaBean.

Used to define the structure of a fact.

  • (deftemplate
    • pattern “A design pattern.”
    • (slot name)
    • (slot type (default “creation”))
    • (slot intent)
    • (slot solution))
asserting facts
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.

all kinds of facts
All Kinds of Facts

;; An ordered fact with no slots – a placeholder that indicates state.


;; A ordered fact of one slot

(assert(weightfactor 0.75))

shadow facts
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.

jess rules
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.
rule syntax
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.
simple rule example
Simple Rule Example

Checking working memory state.

;; A not very useful error handler

(defrule report-error



(printout t “There is an error” crlf))

a more complex rule
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))

more pattern and control tools
More Pattern and Control Tools
  • Literal / variable constraints
  • Logical conditional tests
  • Predicate functions


control and structure

  • Salience
  • Modules
  • Defquery
  • Backward-chaining
break time
Break Time!

Let’s take a quick 5 minute pause…

scripting java from jess
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.
scripting java with jess
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)


demo 1 pat pattern analysis tool
Demo 1: PAT (Pattern Analysis Tool)
  • PAT is a simple decision-tree for choosing a Java design-pattern.
  • Uses an initial interview to establish problem space.
  • Recommends a GoF Java design-pattern to fit the available facts.


the jess api
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)

the rete ree tee object
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.
using the jess api
Using the Jess API…

try {

Rete engine = new Rete();


“printout t “Hello PJUG”);;


catch (JessException je {}

…is simple…all you really do need to do is call one or more Rete methods …

demo 2 catalog servlet
Demo 2: Catalog Servlet

import jess.*;

import javax.servlet.*;

import javax.servlet.http.*;


publicabstractclass BaseServlet extends HttpServlet {

publicvoid doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {

doGet(request, response);



Here is an example of a Jess application running as a Java servlet…

pattern references
Pattern References
  • Shalloway, A., Design Patterns Explained, Addison-Wesley, 2002
  • Gamma, E. et. al., Design Patterns: Elements of Reusable Object-Orient Software, Addison-Wesley, 1995
expert systems references
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
  • Download Jess at:

  • Join the Jess user community at:

  • See Dr. Friedman-Hill’s Jess in Action at:

for further study
For Further Study
  • CLIPS Expert System Shell

  • FuzzyJ Website



Q & A

Thanks for your attention, and I hope that you try Jess!