M. Uschold

THE USE OF PROLOG FOR IMPROVING THE RIGOUR AND ACCESSIBILITY OF ECOLOGICAL MODELLING

Abstract We introduce three concepts that offer considerable benefit to the process of ecological modelling: the descriptive representation of models; the explicit representation of knowledge about how to model; and the development of knowledge-based systems that can help ecologists construct models. Prolog, a computer language based on formal logic, has much to offer in realising these ideas. We introduce the concept of a ‘model blueprint’, a complete, formal specification of the structure of a model, and show how a blueprint can be represented as a Prolog program, basing our analysis on system dynamics models for simplicity. We consider ways in which the Prolog interpreter can be used selectively to retrieve information about the model, to check for errors in the formulation of the model, and to evaluate the model mathematically. However, there are drawbacks with this approach, so we discuss ways of overcoming these by implementing - also in Prolog - programs which buffer the user from the difficulties of working at the level of the Prolog interpreter. These include the generation of descriptions of model structure, and the development of a program to help in the construction of simulation models.

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 EC0 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 lingzur 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. Many ecologists would like to construct computer simulations of ecological systems, but are discouraged by the complexity of current simulation languages. They must learn how to program in an available language (a considerable effort); or describe their model to a sympathetic modelling expert who will then implement their model on their behalf. Our goal is to relieve ecologists of this handicap by providing a computer system which is easy to use and which helps them transform their view of a problem from ecological terms, ultimately to working computer programs. A key part of our research has been the design and testing of various mechanisms for conducting dialogues between humans and computers in order to obtain specifications for working programs. This paper contains an analysis of these dialogue systems. Our central thesis is that, although it is relatively easy to provide interface methods for users familiar with the mathematical formalism upon which a program construction system is based, it is much more difficult to scale up these techniques to