(Deprecated) logical (in insert)

Purpose

This keyword is used within an insert statement to indicate that the object to be inserted in the working memory is of the logical type.

Context

Rule conditions, rule actions, or functions

Description

The insert statement creates a new object of a given class, execute statements on the scope of the object, and inserts the object into the working memory. The logical keyword indicates that the object is of a logical type. A logical object has two properties: the object is unique and the validity of the object is maintained.

To specify the uniqueness of the object, you must redefine the Java™ Object.equals method in your Java class (see the example below). The process goes on as follows:

1. An object is created normally from the specified constructor.

2. This object is then tested by the equals method to determine whether an object that equals this object already exists in the working memory.

   • If an existing object in the working memory equals the object, the new object is not inserted into the working memory. The existing object is set to have a new justification that corresponds to the condition part of the rule that has just been executed.

   • If no existing object in the working memory equals the object, the new object is inserted into the working memory. This object is then maintained by the condition part of the rule that inserted it.

Maintenance of a logical object means that as long as the condition part of a rule that justified the object remains true, the object is kept in the working memory. If the condition part becomes false, the object loses a justification. A logical object that loses its last justification is automatically retracted from the working memory.

To benefit of the Truth Maintenance System, you must redefine the Java Object.equals method and define a hashCode method in your Java class, as follows:

public boolean equals (Object obj)
   {
      if (obj == null || !(obj instanceof className))
         return(false);
         className myObj = (className)obj;
         return (fieldName.equals(myObj.fieldName));
   }
...

public int hashCode()
   {
      return (fieldName.hashCode());
   }