Jess: A Rule-Based Programming Environment

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Jess A Rule-Based Programming Environment
Expert System

• Reporter Yu Lun Kuo
• E-mail sscc6991_at_gmail.com
• Date April 10, 2006

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Why Expert System

• Question of project developer
• Program algorithm Data Structure (Hard)
• Software Engineering
• Demand ? Design ? Coding (Demand Phase)
• Programmer
• Expert Systems
• Rule-based computer programs that capture the
  knowledge of human experts in their own fields of
  experience

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Rules

• A rule is a kind of instruction or command that
  applies in certain situations
• Rules are a lot like the if-then statements of
  traditional programming languages
• if part of a rule is often called its left-hand
  side
• then part of a rule is often called its
  right-hand side
• A rule-based system is a system that uses rules
  to derive conclusions from premises

if predicate or premises then
actions or conclusions
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Rule Engine

• A rule engine doesnt contain any rules until
  they are programmed in
• A rule engine knows how to follow rules, without
  containing any specific knowledge itself
• deployment environment

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Architecture of a Rule-Based System

• A typical rule engine contains
• Inference engine
• Forward Chaining LISP, CLIPS
• Backward Chaining - PROLOG
• Rule base (knowledge base)
• Working memory (fact base)
• Inference engine consists of
• Pattern matcher
• Agenda
• Execution engine

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Pattern Matcher

• The working memory contains thousands of facts,
  and each rule has two or three premises
• The pattern matcher need to search through
  millions of combinations of facts to find those
  combinations that satisfy rules
• All the rules are compared to working memory
• Decide which ones should be activated during this
  cycle

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Agenda

• Inference engine figures out which rules should
  be fired, it still must decide which rule to fire
  first
• The list of rules that could potentially fire is
  stored on the agenda
• Ex.

Give high priority
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Execution Engine

• The execution engine is the component of a rule
  engine that fires the rules
• Some modern rule engines offer a complete
  programming language you can use define
• What happen when a give rules fires

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Conflict Set
Conflict Resolution
Fired
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Jess (Java Expert System Shell)

• The Java Rule Engine API defined by the
  javax.rules package
• A standard enterprise API for accessing rule
  engines
• Site http//www.jcp.org/jsr/detail/94.jsp
• Jess rule engine
• A rule engine and scripting language developed at
  Sandia National Laboratories in Livermore,
  California in the late 1990s
• It can access to all of Javas powerful APIs for
  networking, graphics, database access, and so on

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Jess (Cont.)

• The Jess language can directly access all Java
  classes and libraries
• This allows you to experiment with Java APIs
  interactively and build up large programs
  incrementally
• Jess is therefore useful in a wide range of
  situations
• Jess can be used in command-line applications,
  GUI applications, servlets, and applets.

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• The most important step in developing a Jess
  application is to choose an architecture
• Pure Jess language, with no Java code
• Pure Jess language, but the program accesses Java
  APIs
• Mostly Jess language code, but with some custom
  Java code in the form of new Jess commands
  written in Java
• Half Jess language code, with a substantial
  amount of Java code providing custom commands and
  APIs. Jess provides the main() function
• Half Jess language code, with a substantial
  amount of Java code providing custom commands and
  APIs. You write the main() function
• Mostly Java code, which loads Jess language code
  at runtime
• All Java code, which manipulates Jess entirely
  through its Java API

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Scripting Java with Jess

• From Java code, you can access all parts of the
  Jess library
• Easy to embed Jess in any Java application
• Use Jess for experimenting with Java APIs
• Jess is therefore a kind of scripting language
  for Java
• You can create the windows, buttons, and other
  graphical components with a few lines of Jess code

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Representing facts in Jess

• The contents of Jesss working memory are held in
  your computers RAM
• Most other constructs in Jess, facts are stored
  as lists
• Jess offers a set of functions to let a program
  perform the basic collection operations on the
  working memory
• add, remove, modify, duplicate

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Working memory

• assert Add facts to working memory
• Clear Clears all of Jess
• Deffacts Defines the initial contents of
  working memory
• Facts Display the content of working memory
• Reset Initializes the working memory
• Retract Removes facts from working memory
• Watch Tells Jess to print diagnostics when
  interesting things happen