Practical rules for reduction on the number of states of a state diagram

Many object-oriented modeling methods adopt state-based formalisms to specify the behavior of objects. State-based formalisms, pioneered by David Harel (1987), are a powerful and yet intuitive tool in modeling the dynamics of objects. However, when a real world object has a huge number (or an infinite number) of states, we usually have to map them into a relatively small number of states in practice. This mapping has been done intuitively and heuristically by software designers. There has not been a set of general and systematic rules for this mapping. We focus on exploring a set of such rules with which a system of a large number (or an infinite number) of states can be transformed systematically into an equivalent finite-state system with a smaller number of states. Examples are given and the suggested rules are explained.