Applications using the API
When there is a need to create or edit a graph, users should use an external graph editor application to do this interactively based on the visualization of a graph. The graph editor is an external program that communicates with uDraw(Graph); using the API (application programming interface). The editor or any other uDraw(Graph) application is responsible for controlling and manipulating the structure of a graph.
Applications can be connected to the API with the File menu or with command line options. At start time the editor adds some menus and icon buttons to uDraw(Graph)'s user interface to enable inserting or deleting nodes and edges or changing their attributes. Application menus can be attached to the Edit menu, but there is no built-in function behind these menus in uDraw(Graph). Instead, the API sends menu events to the graph editor application to inform about user interactions. For example, when the user selects a node (1. event) and chooses the previously attached menu 'Edit/Delete Node' (2. event), then the editor knows by these two events that the user would like to remove the specified node. The editor has an own graph data structure which has to be modified in order to reflect the events. After modification, the editor sends the actual graph back to uDraw(Graph) to update the visualization.
This principle can be used by any application program that is connected to uDraw(Graph)'s API. Note that the application is exclusively responsible for controlling the graph structure. uDraw(Graph) is unable to modify the graph on its own. This is important when uDraw(Graph) is the graph user interface on top of an arbitrary application program. On the other side, by separating the representation layer (uDraw(Graph)) from the control layer (application connected to the API), the application programmer is relieved from dealing with graph layout algorithms and computer graphics.
Next: Graph Layout.
