This part of the book describes behavior notations. Behavior and communication are two complementary functional aspects of the services provided by the system. Behavior concerns the ordering of interactions in time; communication concerns the information exchange between systems during interactions. All behavior notations can be used at various degrees of formality, ranging from rough, incomplete sketches to fully formal executable descriptions.

• Chapter 11. I introduce event lists and state transition tables (STTs), which are tabular notations for behavior. These are easy to use and can grow to any size because we can simply continue on the next paper. However, they do not represent the structure of behavior very well.

• Chapter 12. I introduce the two major state transition diagram (STD) techniques: Mealy diagrams, used in Yourdon-style structured analysis, and statecharts, used in Statemate and most object-oriented methods. Any STT can be transformed into an equivalent STD and vice versa. Unlike STTs, STDs cannot grow to any size because paper size is finite. However, they can represent the structure of behavior rather well.

• Chapter 13. I list the choices to be made if we want to give precise semantics for STTs and STDs. These choices must be made if you want to be able to execute an STT or STD. This chapter can be skipped if you do not want to make the meaning of behavior descriptions precise.