/****
 *
 * Class BoxArrow is a very simplistic model of data that will be viewed in a
 * box arrow diagram.  Here we have Node and Link classes that are viewed as
 * boxes and arrows, respectively.
 *
 * Users of the box-arrow view class may subclass from Node and Link if model
 * specs make such subclassing appropriate.  Otherwise, box-arrow users may use
 * the design and implementation of the Node and Link classes as guides to
 * establish an appropriate model/view relationship with the box-arrow view
 * class.
 *
 */