The importance of structuring, ie, of creating aggregates of different objects in interactive programs, has long been recognized in computer graphics. All graphics packages provide some form of aggregation, like structures in PHIGS[12], the scene database of IRIS Inventor[27], or the so called Go trees in GoPATH[7]. Although the structures used in these examples are all relatively simple (directed acyclic graphs or just trees), the appearance of hypertext and, lately, of hypermedia systems makes it clear that more general aggregation facilities are also necessary.
To answer these demands, the MADE toolkit includes a general graph management facility in the form of graph objects. These objects allow for the specification, management, and the traversal of general graphs, with no restrictions imposed on their types. Nodes of these graphs may refer to any MADE object. Graph management is achieved via special MADE objects; consequently, recursive graphs may also be defined via the same mechanism. Individual MADE objects can be referred to by several graph nodes (ie, they can be shared).
Graph objects provide a sound basis for the type of structuring required by graphics as well as for complex hypermedia navigation systems. They are fully integrated into the full MADE structure, which has a number of advantages. As an example, graphs provide an automatic defence against concurrent access of structures by active objects, they can be exported and imported using the very same mechanism as for all other MADE objects (ie, complete structures may be stored in databases), etc.