A visual language for the design of structured graphical objects

The design of abstract or physical structures has much in common with the design of software structures, particularly when the structure in question has a mechanical or computational behaviour; such as a digital circuit. Like programming language systems, design systems must have expressive power sufficient for representing any design, a simulation mechanism for debugging the artifact under construction, and a production mechanism; for example, compilation for a programming language, or chip fabrication for a VLSI design system. Since specifying complex devices requires repetitive and conditional structures analogous to iteration, recursion and conditionals in programs, languages for designing complex devices are usually based on textual programming languages, for example VHDL for VLSI design. The advent of full featured visual programming languages, however raises the possibility that the mechanisms used to visually express compact and powerful program structures could be generalised to design languages. We consider using these mechanisms to express the design of structured graphical objects