Designing and prototyping in grads

We present a graphical approach to software design that supports specification, prototyping, stepwise refinement and analysis of designs. The approach is based on a formal model from language and graph theory and has a practical implementation. In the examples given we demonstrate that dataflow methods of design can be conveniently combined with state machine diagrams within a prototyping environment. We also show how complex designs may be decomposed into independent modules. Finally we include an example formal specification of a system based on the same graphical design approach.