What is simple to complex model progression?

Simple to complex model progression is used to gradually unfold the characteristics of the domain. Usually the first model progression level is a very simple model with only a few of the variables represented. Later on more domain characteristics are added eventually yielding a complete description of the domain.

To enable model progression the domain should be decomposable in different levels of complexity. That is, it should be possible to identify subsystems (by leaving out variables and relations) that are simpler than the complete system, and that are still a sensible representation. Consistency should be maintained between levels, that is statements that are true one level in the progression, should be true on a higher level, unless directly influenced by new domain characteristics. In the latter case the learner should be made aware of this change.