A (mathematical) model is the representation of a process or system. It contains a set of parameters and mathematical equations related to each other, in order to describe the behavior of such process or system. A model consisting of several interconnected compartments is equivalent to a system of coupled ordinary differential equations (ODE).
The models of MERLIN-Expo are constructed by combining smaller models, referred to as sub-models or sub-systems which make up the MERLIN-Expo model library.