Chapter 2 - A Crash Course in UML State Machines

Abstract

This chapter introduces UML state machines that represent the current state of the art in the long evolution of these techniques. The main challenge in programming event-driven systems is to identify the appropriate actions to execute in response to a given event. In general, the actions are determined by two factors: by the nature of the event and by the current context. The traditional techniques, such as the event action paradigm, neglect the context and result in code riddled with a disproportionate amount of convoluted conditional logic that programmers call “spaghetti” code. Techniques based on state machines are capable of achieving a dramatic reduction of the different paths through the code and simplification of the conditions tested at each the event-action paradigm is applied locally within each state. The concept of state is a very useful abstraction of system history, capable of capturing only relevant sequences of stimuli. In extended state machines, state corresponds to qualitative aspects of system behavior, whereas extended state variables correspond to the quantitative aspects.