Package rp.util.dom

This package implements a framework for storing objects and their relationships.

See:
Description

Interface Summary

DOMObject.Iterator	Used to iterate across DOMObjects.
DOMRelation.Endpoint.Iterator	Used to iterate across the endpoints of a relationship.
DOMRelation.Instance.Iterator	Used to iterate across the instances of a relationship.

Class Summary

DOMObject	The common baseclass for all DOM objects and relations.
DOMRelation	This class represents meta-information about DOM relations.
DOMRelation.Endpoint	The end-point (left or right) of a relationship.
DOMRelation.Instance	Baseclass for relationship instances.
DOMRelation.Left	The left endpoint of a relationship.
DOMRelation.Right	The right endpoint of a relationship.

Package rp.util.dom Description

This package implements a framework for storing objects and their relationships.

There are two main baseclasses, DOMObject and DOMRelation. DOMObject is a baseclass for any type of domain object, e.g.,

package rp.util.dom.test;
import rp.util.dom.*;
class Person extends DOMObject {
    private String name;
    public Person(String name) { this.name = name; }
    public String getName() { return name; }
}

DOMRelation is not a baseclass. Instances of DOMRelation contain meta-information about relationships, e.g.,

private static DOMRelation metainfo = new DOMRelation("IsBossOf");
static {
    metainfo.setLeftClassName("rp.util.dom.test.Manager");
    metainfo.setRightClassName("rp.util.dom.test.Employee");

    metainfo.setLeftName("manages");
    metainfo.setRightName("is managed by");

    metainfo.setLeftNumericity(1,1);  // sets min and max numericty on the left side
    metainfo.setRightNumericity(2,MANY);  // sets min and max numericty on the right side
}

DOMRelation nests a set of related classes used to implements relationship instances. These are:

• Instance: represents an instance of a relationship that links a left DOMObject with a right one. Subclasses will define particular types of relationships, that can possible carry attributes and engage in their own relationships. An important duty of the subclass is to implement the getRelation() method which returns the DOMRelation meta-data necessary to enforce checking of relation semantics.
• Left: represents the left endpoint of a relationship. Each DOMObject participating on the left side of a relationship must allocate one of these to hold the instances. Subclasses will inherit from Left and define the getRelation() method.
• Right: analogous to Left
• Endpoint: because of the commonality, both Left and Right inherit from Endpoint.

In addition, various iterators classes are defined. By convention, a class 'Iterator' defined as a static contained class of a class X will iterate over objects of type X. Therefore a DOMObject.Iterator iterates over DOMObjects, a DOMRelation.Iterator iterates over DOMRelation meta-objects, a DOMRelation.Instance.Iterator iterates over instances of relations, and a DOMRelation.Endpoint.Iterator iterates over Endpoints (left or right).

Below is an example that shows how to define and establish a relationship.

package rp.util.dom.test;

import rp.util.dom.*;

class Person extends DOMObject {
    private String name;
    public Person(String name) { this.name = name; }
    public String getName() { return name; }
}

class Manager extends Person {
    public IsBossOf.Left employees = new IsBossOf.Left(this);
    public Manager(String name) { super(name); }
}

class Employee extends Person {
    public IsBossOf.Right manager = new IsBossOf.Right(this);
    public Employee(String name) { super(name); }
}

class IsBossOf extends DOMRelation.Instance {
    private static DOMRelation metainfo = new DOMRelation("IsBossOf");
    static {
	metainfo.setLeftClassName("rp.util.dom.test.Manager");
	metainfo.setRightClassName("rp.util.dom.test.Employee");

	metainfo.setLeftName("manages");
	metainfo.setRightName("is managed by");

	metainfo.setLeftNumericity(1,1);  // sets min and max numericty on the left side
	metainfo.setRightNumericity(2,MANY);  // sets min and max numericty on the right side
    }
    public static DOMRelation get() { return metainfo; }
    public        DOMRelation getRelation() { return metainfo; }

    // an example of an attribute on a relation. DOMRelation.Instance extends DOMObject.
    public java.util.Date whenStartedManaging;

    // Establish a relationship between m and e
    public IsBossOf(Manager m, Employee e) {
	super(m.employees, e.manager);
    }

    static class Left extends DOMRelation.Left {
	public Left(DOMObject o) { super(o); }
	public DOMRelation getRelation() { return metainfo; }
    }

    static class Right extends DOMRelation.Right {
	public Right(DOMObject o) { super(o); }
	public DOMRelation getRelation() { return metainfo; }
    }
}

public class Test {
    public static void main(String args[]) {
	Manager sally = new Manager("Sally");
	Employee jack = new Employee("Jack");
	Employee jill = new Employee("Jill");

	new IsBossOf(sally,jack);
	new IsBossOf(sally,jill);

	for(DOMObject.Iterator i = sally.employees.iterator(); i.hasNext(); )
	    System.out.println( ((Employee)i.next()).getName() );
    }
}