Interaction between objects

The following short sketch explains what happens, if Mosaic loads a new document. The event flow between different classes of the functional units of Fig. 7 is shown in Fig. 8. The parenthesized numbers in the following paragraph label the ``event-arrows'' in Fig. 8:

After being informed by Mosaic (1), the Communication-object sends an event to the EventDispatcher (2) which forwards this event to the Navigator-object (3). This object may trigger the creation of a new topology object (4)(5). A change of the topology propagates to one (or more) layout objects (6)(7), leading to a recalculation of the node positions. These new node positions are reported to the visualization objects (canvas widget objects), causing an update of the screen image (8)(9).

Besides the topology objects, several history objects which implement different history strategies (not shown in Fig. 8) may react to the events of the navigator. Such history strategies are, for example:

1. complete history including all back steps as well as normal moves.
2. optimized history containing the shortest path from the starting node to the current node.
3. age history corresponds to the node numbers displayed in a window (see page ).
4. root path uses the path consisting of tree-edges leading from the current node to the root node.