The ECO program construction system: ways of increasing its representational power and their effects on the user interface

There is a growing interest in programs which help users with little experience of computing to construct simulation models. Much recent development work on such systems has utilized comparatively simple mathematical methods (such as system Dynamics) to facilitate the development of a friendly user interface. The problem with these simple modelling languages is that they assume that users have preconceived ideas of the simulation models which they want to build. In the ECO project, which involved the construction and testing of programs to help ecologists build simulation models, it became clear that users could not always adapt their ideas to fit into these mathematical frameworks. They required a more expressive input language in which to describe their modelling problems, rather than being forced directly to specify the programs which solved those problems. However, we found that as the input language became more sophisticated the complexity of the user interface became disproportionally larger. We attempt to clarify the reasons for this phenomenon by comparing the various systems which we built to try to solve this problem. This comparison is facilitated by the use of a sorted logic as a lingua franca for the various formalisms used in each system. Our analysis centres around a small number of key characteristics which we use to highlight the strengths and weaknesses of various dialogue techniques.