Mostly adopted from Jason Morris notes (Morris Technical Solutions)

 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 Base (knowledge base)  Working Memory (fact base)  Inference Engine (rule engine)

 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.

 Match the facts against the rules.  Choose which rules to fire.  Execute the actions associated with the rules.

 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 algorithm to match patterns.  Rete network = an interconnected collection of nodes = working memory.

WORKING MEMORY RULE BASE EXECUTION ENGINE INFERENCE ENGINE PATTERN MATCHER AGENDA

 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.

(printout t “Hello Class!” crlf) Your very first Jess program!

 (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:

 Named containers that hold a single value  Untyped  Begin with a ? mark  Can change types during lifetime  Assigned using bind function

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

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

(deffunction area-sphere (?radius) “Calculate the area of a sphere” (bind ?area (* (* (pi) 2)(* ?radius ?radius))) (return ?area))

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

 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.

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

;; 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))

 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.

 … 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.

 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.

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

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

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

(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 ) ((?*frame* getContentPane) add ?*button*) (?*frame* setVisible TRUE)

 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 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.

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

 Download Jess at:  Join the Jess user community at:  See Dr. Friedman-Hill’s Jess in Action at:  CLIPS Expert System Shell  FuzzyJ Website