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Jess: A Rule-Based Programming Environment

Jess: A Rule-Based Programming Environment. Expert System. Reporter: Yu Lun Kuo E-mail: sscc6991@gmail.com Date: April 10, 2006. Why Expert System. Question of project developer Program = algorithm + Data Structure (Hard) Software Engineering Demand  Design  Coding (Demand Phase)

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Jess: A Rule-Based Programming Environment

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  1. Jess: A Rule-Based Programming Environment Expert System Reporter: Yu Lun Kuo E-mail: sscc6991@gmail.com Date: April 10, 2006

  2. 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

  3. 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

  4. Rule Engine • A rule engine doesn’t contain any rules until they are programmed in • A rule engine knows how to follow rules, without containing any specific knowledge itself • deployment environment

  5. 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

  6. 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 activatedduring this cycle

  7. 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

  8. 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

  9. Conflict Set Conflict Resolution Fired

  10. 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 Java’s powerful APIs for networking, graphics, database access, and so on

  11. 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.

  12. 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

  13. 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

  14. Representing facts in Jess • The contents of Jess’s working memory are held in your computer’s 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

  15. 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

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