A graph based framework for the implementation of visual environments

We propose an architecture for storing visual expressions within an environment which supports various forms of visual expression editing, like syntax directed editing, free editing, and layout editing. The proposed architecture is based on two related graph data structures: an abstract syntax graph represents the logical structure of a visual expression in terms of its visual language syntax; a spatial relations graph represents the pictorial structure of a visual expression with graphical objects as nodes and spatial relations as edges. We explain the distinction between the two ways of structuring in detail, we show how coupled graph grammars can be used to define, build and relate the two structures, and we explain how an editor for a visual language can be defined on top of these data structures. We use the visual language Message Sequence Charts (MSC) as a running example.