Jess Introduction

Jess, Java Expert System Shell

Originally a core Clips implementation in Java
Evolved into Java-influenced environment, details refer to Jess

Extendable

can be extended using Userfunction

Java program:

import jess.*;

public class ExMyUpcase implements Userfunction
{
    // The name method returns the name by which the function will appear in Jess code.
    public String getName() { return "my-upcase"; }

    public Value call(ValueVector vv, Context context) throws JessException
    {
        return new Value(vv.get(1).stringValue(context).toUpperCase(), RU.STRING);
    }
}

Every datum in Jess is represented by an object of jess.Value. The jess.Context represents an execution context for the evaluation of function calls and the resolution of variables. The jess.ValueVector class is Jess's internal representation of a list, and is used to represent multifields.

Jess commands:

Jess> (load-function ExMyUpcase)
Jess> (my-upcase foo)

Embeddable

can embeded in a Java program:

    import jess.*;
    public class ExPt
    {
        public static void main(String[] unused) throws JessException
        {
            Rete r = new Rete();
            r.executeCommand("(batch jess/scriptlib.clp)");
            r.executeCommand("(deftemplate point \"A 2D point\" (slot x) (slot y))");
            r.executeCommand("(assert (point (x 37) (y 49)))");
            r.executeCommand("(facts)");
        }
    }

Executing a Jess File

    import jess.*;

    // ...

    // Create a Jess engine
    Rete rete = new Rete();

    // Open the file test.clp
    FileReader fr = new FileReader("test.clp");

    // Create a parser for the file, telling it where to take input
    // from and which engine to send the results to
    Jesp j = new Jesp(fr, rete);
    try
    {
        // parse and execute one construct, without printing a prompt
        j.parse(false);
    }
    catch (ReteException re)
    {
        // All Jess errors are reported as 'ReteException's.
        re.printStackTrace(rete.getErrStream());
    }

Example 1: fixed rule-base file name

Java source: Test.java
Jess source: Hello1.clp

Example 2: user-specified rule-base file name

Java source: Test2.java
Jess source: Hello.clp

Object Support

Create and manipulate Java objects directly from Jess,

   (bind ?ht (new java.util.Hashtable))
   (call ?ht put "key1" "element1")
   (call ?ht put "key2" "element2")
   (call ?ht get "key1")

Run-time Environment

1. Command Line

    java jess.Main

2. Graphics Console

    java jess.Console