The dynamic model describes the behaviour of a distributed parameter system in terms of how one qualitative state can turn into another. A qualitative state is described by a static model, i.e. the distributions and intersections of the qualitative fields at a particular time instant or interval.
The dynamic model is inspired by the process-based ontology of QPT. However, since QPT was developed mainly for lumped object-based models, the concepts have been modified in several ways to fit the framework of the static model, i.e. in order to describe changes to qualitative fields rather than to objects.
The processes are divided into two types, temporal and spatial, as follows:
The dynamic spatio-temporal behaviour of the system is thus modelled as a collaboration between temporal and spatial processes. The terms spatial and temporal have been chosen to emphasize the conceptual difference between the two types of processes. However, a temporal process also has a spatial extent, which is defined by the region where it is active. Likewise, a spatial process has a temporal extent defined by the time it takes to spread an influence through space.
Since a spatial extent can be defined for both types of processes, they can be represented as qualitative fields. The process structure of the system at each instant is thus a qualitative state treated in the same way as the parameter fields. This results in a coherent representational framework, which has several advantages both where comprehension and implementation are concerned.