UNDO FEATURE FOR A GRAPHICAL PROGRAMMING SYSTEM

An Undo/Redo feature for a graphical programming system which minimizes the required data storage. The graphical programming system includes a plurality of interconnected objects, including fixed size objects and variable size objects. A variable size object is an object which typically changes in size, i.e., grows or shrinks, in response to user modification, whereas fixed size objects do not change in size. When an object is modified by the user, the method of the present invention stores a backup copy for undo purposes. For modification of an object, the backup is performed differently depending on whether the object is a variable size object or a fixed size object. For a variable size object, the method stores the original object as the previous object in the backup list, and the method stores a copy of the original object as the current object in the backup list. For a fixed size object, the method stores a copy of the original object as the previous object in the backup list, and the method stores the original object as the current object in the backup list. For a fixed size object, the original object thus remains as the current or foreground object in the graphical program. Since the original object stays in the foreground, other objects which reference this object maintain their references, and thus are not also required to be backed up. Therefore, the present invention provides a unique system and method for performing undo/redo in a graphical system which minimizes the amount of memory required for undo purposes.