intro to jess

7/30/2019 Intro to Jess

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Intro to JessThe Java Expert System

Shell

By Jason Morris

Morris Technical Solutions


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Quotable Quotes

Each problem that I solved

became a rule which servedafterwards to solve otherproblems.- Rene Descartes


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Quotable Quotes

As a rule we disbelieve allthe facts and theories forwhich we have no use.

- William James


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Quotable Quotes

Hell, there are no rules here --

we're trying to accomplish

something.- Thomas A. Edison


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Quotable Quotes

Get your facts first, and then

you can distort them as muchas you please.- Mark Twain


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Quotable Quotes

If the facts don't fit the

theory, change the facts.- Albert Einstein


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Quotable Quotes

There are two rules

for success:

1) Never tell

everything you know.- Roger H. Lincoln


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Quotable Quotes

Facts do not cease to

exist just because theyare ignored.

-Aldous Huxley


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Agenda

What are expert systems?

What are rule-based expertsystems?

Introduction to Jess

The Jess Language

5 minute break


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Agenda

Scripting & The Jess API

Demo 1 : Design Pattern Expert Demo 2 : Catalog Servlet

References and Further Study

Q & A


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Expert Systems

Are a branch ofartificialintelligence.

Simulate human reasoning in somedomain.

Reason by heuristic or

approximate methods. Explain and justify solutions inuser-friendly terms.


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Types Of Expert Systems

Neural Networks

Blackboard Systems

Belief (Bayesian) Networks

Case-Based Reasoning Rule-Based Systems


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Rule-Based Expert Systems

Originated from AI research in the70s and 80s.

Problem data stored as facts. Reason using IFTHENELSE

rules.

Can reason deductively (forward-chaining) or inductively(backward-chaining).


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When to Use Rule-Based

Systems Problem Domain = narrow, well-

understood domain theory

Knowledge Representation = factsand rules

Output = recommendation

Explanation = rule firing trace Learning Ability= generally no (but)


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Inference Process

1. Rules and facts compared usingpattern matcher.

2. Matched rules activated into aconflict set.

3. Conflict set resolved into agenda(process called conflict resolution).

4. Rule engine fires on agenda.5. Engine cycles until all rules are

satisfied.


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The Java Expert System Shell

Developed at Sandia NationalLaboratories in late 1990s.

Created by Dr. Ernest J. Friedman-Hill.

Inspired by the AI production rule

language CLIPS. Fully developed Java API forcreating rule-based expertsystems.


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Rule-Based Expert System

Architecture

Rule Base (knowledge base)

Working Memory (fact base)

Inference Engine (rule engine)


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Inference (Rule) Engines

Pattern Matcher decides whatrules to fire and when.

Agenda schedules the order inwhich activated rules will fire.

Execution Engine responsible

for firing rules and executing othercode.


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Inference Process

Match the facts against the rules. Choose which rules to fire.

Execute the actions associated

with the rules.


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How Does Jess Work?

Jess matches facts in the fact base torules in the rule base.

The rules contain function calls thatmanipulate the fact base and/or otherJava code.

Jess uses the Rete (ree-tee) algorithm

to match patterns. Rete network = an interconnectedcollection of nodes = working memory.


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Jess Architecture Diagram

WORKING

MEMORY

RULEBASE

EXECUTION

ENGINE

INFERENCE

ENGINE

PATTERN

MATCHER

AGENDA


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Procedural Programming

Traditional programming (BASIC,C, FORTRAN, Pascal, etc.).

Largely based on functions.

Programmer controls logic.

Sequential and deterministic.

Object-oriented programming isprocedural within object methods.


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Declarative Programming

New programming paradigm -rules.

Programmer does not reallycontrol code logic.

Rule engine finds most efficientpath of code execution.

Replaces hard to maintain nestedIFTHENELSE coding.


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Wait a minute!

Wellyes andnobut dont worry,Calvin!

What? II

cant control

my code??


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Thought Experiment

Imagine writing a procedural/OOPalgorithm to solve ajigsaw

puzzle. 500+ pieces, different shapes and

colors.

Polymorphism runs amok!

Yet we manage to solve thepuzzle


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Intuition and Rules

Dump the puzzle pieces on a cardtable in no particular order.

Your brain instinctivelybegins toapply rules to solve the puzzle!

What might this look like in code?


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Intuitive Inferencing

(corner_found(piece_is_corner)

=>(assert corner-found)(save_piece))

(edge_found

(piece_is_edge)=>(assert edge-found)(save_piece))

Your brainknows what todo with a cornerpiece

and an edgepiece.


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Whats Going On

Your brain recalls rules orheuristics to solve the problem.

Your brain pattern-matches,prioritizes, and applies rulesaccording to the facts in memory.

A particular solution algorithmemergesas rules fire on facts.


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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.


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Obligatory Tradition

(printoutt Hello PJUG-ers! crlf)

Your very first Jess

program!


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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:


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Jess Variables

Named containers that hold asingle value.

Untyped. Begin with a ? mark.

Can change types during lifetime.

Assigned using bind function.


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Jess Variables and Lists

EXAMPLE: Adding two numbers

(bind?x 2) ; assign x = 2

(bind?y 3) ; assign y = 3(bind?result (+ ?x ?y)) ; findsum

Everything is a list in Jess!


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Control Flow

foreach

if/then/else

while

apply

build

eval

progn

Common Jess-specific


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Jess Functions

(deffunction get-input()Get user input from

console.

(bind?s (read))(return ?s))

Even functions are lists.


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Jess Function Example

(deffunction area-sphere(?radius)

Calculate the area of a

sphere

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

(return ?area))


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Jess Function Example

(printout t "The surfacearea of a radius = 2 meter

sphere is " +(area-sphere 2) + " m^2")

How do we use this in Jess?


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Working With Facts

Facts have a head and one ormore slots.

Slots hold data (can be typed). Multislots can hold lists.

You can modify slot values at

runtime. Facts are constructed from

templates.


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Jess Fact Types

Ordered head only.

Ordered single slot. Unordered multiple slot, like a

database record.

Shadow slots correspond toproperties of a JavaBean.


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Deftemplate

Used to define the structure of a fact.

(deftemplatepattern A design pattern.(slot name)(slot type (defaultcreation))(slot intent)(slot solution))


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Asserting Facts

;; Asserting a new patternfact.

(printoutt Enter pattern

name: crlf)(bind?x getInput)(assert pattern (name ?x))

Facts store the initial conditions.


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All Kinds of Facts

;; An ordered fact with no

slots a placeholder thatindicates state.

(assert(answer-is-valid))

;; A ordered fact of one slot

(assert(weightfactor 0.75))


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Shadow Facts

defclasscreates a deftemplate

from a bean. definstanceadds bean to

working memory.

Shadow facts are unordered factswhose slots correspond to the

properties of a JavaBean.


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Jess Rules

are the knowledge-base of thesystem.

fire only once on a given set offacts.

use pattern constraints tomatch facts.

are much faster than IF-THENstatements.


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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.


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Simple Rule Example

;; A not very useful error handler(defrule report-error

(error-is-present)=>

(printoutt There is an errorcrlf))

Checking working memory state.


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A More Complex Rule

;; A more useful error handler(defrule report-err?err (printout t "Error was: " ?msg crlf)(retract ?err))

Using pattern bindings in rules.


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More Pattern and Control

Tools

Literal /variableconstraints

Logical

conditionaltests

Predicatefunctions

Salience Modules

Defquery

Backward-

chaining

matching control and structure


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Break Time!

Lets take a quick 5minute pause


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Scripting Java from Jess

You can interactively access allJava APIs from Jess.

This makes exploring Javasomewhat easier and immediate.

No code, compile, debug cycle.


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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 myPJUG"))

(?*frame* setSize 500 300)((?*frame* getContentPane) add ?*button*)

(?*frame* setVisible TRUE)

swingDemo.bat


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Demo 1: PAT

(Pattern Analysis Tool) PAT is a simple decision-tree for

choosing a Java design-pattern.

Uses an initial interviewtoestablish problem space.

Recommends a GoF Java design-

pattern to fit the available facts.

examples/pattern.clp


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The Jess API

jess - inference engine guts.

jess.awt GUI wrappers.

jess.factory - Allows extensionsthat get into the guts of Jess.

Organized into 3 packages, 64classes (not hard to learn)


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The Rete (ree-tee) Object

The reasoning engine and thecentral class in the Jess library.

Executes the built Rete network,and coordinates many otheractivities.

Rete is essentially a facade for theJess API.


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Using the Jess API

issimpleall

you really doneed to do iscall one or

more Retemethods

try {

Rete engine = new

Rete();engine.executeCommand(

printout t Hello PJUG);

engine.run();}

catch (JessException je {}


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Demo 2: Catalog Servlet

import jess.*;

import javax.servlet.*;

import javax.servlet.http.*;

import java.io.*;

publicabstractclass BaseServletextends HttpServlet {

publicvoiddoPost(HttpServletRequestrequest, HttpServletResponseresponse) throws IOException,ServletException {

doGet(request, response);

}

}...

Here is an

example of aJessapplicationrunning as aJava servlet


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Pattern References

Shalloway, A., Design PatternsExplained, Addison-Wesley, 2002

Gamma, E. et. al., DesignPatterns: Elements of ReusableObject-Orient Software, Addison-

Wesley, 1995


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Expert Systems References

Friedman-Hill, E. J.,Jess InAction, Manning Press, 2003

Jackson, P., Introduction toExpert Systems 3rdEd., Addison-Wesley, 1999

Giarratano, J., Expert Systems:Principals and Programming, PSW-Kent, 1989


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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.s

html

See Dr. Friedman-Hills Jess in

Action at:http://www.manning.com/friedman-hill/
http://herzberg.ca.sandia.gov/jess/index.shtmlhttp://herzberg.ca.sandia.gov/jess/mailing_list.shtmlhttp://herzberg.ca.sandia.gov/jess/mailing_list.shtmlhttp://www.manning.com/friedman-hill/http://www.manning.com/friedman-hill/http://www.manning.com/friedman-hill/http://www.manning.com/friedman-hill/http://herzberg.ca.sandia.gov/jess/mailing_list.shtmlhttp://herzberg.ca.sandia.gov/jess/mailing_list.shtmlhttp://herzberg.ca.sandia.gov/jess/index.shtml


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For Further Study

CLIPS Expert System Shell

http://www.ghg.net/clips/CLIPS.html

FuzzyJ Websitehttp://www.iit.nrc.ca/

IR_public/fuzzy/

fuzzyJToolkit2.html
http://www.ghg.net/clips/CLIPS.htmlhttp://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.htmlhttp://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.htmlhttp://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.htmlhttp://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.htmlhttp://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.htmlhttp://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.htmlhttp://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.htmlhttp://www.iit.nrc.ca/IR_public/fuzzy/fuzzyJToolkit2.htmlhttp://www.ghg.net/clips/CLIPS.html


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Q & A

Thanks for yourattention, and Ihope that you

try Jess!

intro to jess

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