Model transformation rules and model disaggregation

Ecosystem models vary considerably in their degree of disaggregation: the extent to which they 'lump' or 'split' model components. However, the criteria for the degree of disaggregation in a model are frequently not clear. The development of such criteria would be enhanced if the degree of disaggregation in a model could be easily changed, permitting a ready comparison of the alternative versions. In this paper, a framework is proposed for representing model transformation rules. Each rule indicates how a particular model component or set of components can be replaced by more- or less-disaggregated components. These rules have the potential to automate the process of generating alternative versions of a model differing in degree of disaggregation, and provide a framework within which modellers can express their expert opinion on the legality, costs and benefits of particular lumping or splitting decisions. The approach is wholly dependent on the symbolic representation of model structure, since each transformation rule is in effect a symbolic re-write rule, expressing how the set of symbols defining one model can be replaced by another set defining an alternative model. It is proposed that the logic programming language Prolog is suitable both for representing model structure in symbolic form, and for representing the model transformation rules.