GDL is an ASCII text representation of a graph. It describes a graph in terms of nodes, edges, subgraphs and attributes. A subgraph is described as a normal graph except that it is specified inside another graph, meaning graph specifications can be nested. aiSee provides special operations for subgraphs such as folding to a summary node, boxing, clustering, or wrapping.
Graphs, nodes and edges may have attributes that specify details of their appearance on the screen such as colors, sizes, shapes etc.
There is always only one top-level graph.
It is also possible to specify regions that are to be initially folded after starting aiSee.
aiSee also accepts the #line directives of the C preprocessor. The macro processing facilities of the C preprocessor offers some tricky possibilities for graph specifications. For example, using a macro directive would enable different languages for node labels to be chosen.