The main aim of this chapter is to argue that semiotics can serve as a theoretical framework for programming computer systems (on semiotic approaches to systems design, see Rasmussen, 1986; Kaasbøll, 1986; Nadin, 1988; Holmqvist & Bøgh Andersen, 1991; Bøgh Andersen, 1990a; Figge, 1991; Boland, 1991; Stamper, 1992). The reason is that although computers are machines, they are not ordinary machines, assembled with bolts and screws. They are symbolic machines constructed and controlled by means of signs.

The interface of the systems is an obvious example of a computer-based sign, but underneath the interface, in the intestines of the system, we also find signs. The system itself is specified by a program text (a sign since it stands for the set of possible program executions to the programmer). The actual execution involves a compiler or interpreter that directly or indirectly controls the computer by means of the program text, and since the compiler is based on a text standing for the set of permissible program texts, a part of the compiler is a meta-sign that – in some versions – very much resembles ordinary grammar.

If we continue this descent through the different layers of the system, passing through the operating system and the assembly code down to the actual machine code, we will come across signs most of the way down.