Object-oriented concepts are fundamental to software design. Object-oriented design refers to software systems that are designed using the concepts of information hiding, classes, and inheritance. Objects are instantiated from classes and are accessed through operations, which are also referred to as methods.

A class is designed using the information hiding concept to encapsulate different kinds of information, such as details of a data structure or state machine. These classes are originally determined during the object and class structuring phase of analysis modeling, as described in Chapter 8. In particular, this chapter describes the design of class interfaces and the operations provided by each class. This chapter also describes the use of inheritance in software design. An introduction to information hiding, classes, and inheritance was given in Chapter 4. As pointed out in Chapter 4, the term operation refers to both the specification and the implementation of a function performed by an object.

Section 14.1 gives an overview of the concepts, architectures, and patterns used in designing sequential object-oriented architectures. Section 14.2 describes important issues in the design of information hiding classes. Section 14.3 describes the design of the class interface and operations, as well as how they are determined from the dynamic model. The following sections describe the design of different kinds of information hiding classes: Section 14.4 describes the design of data abstraction classes, which encapsulate data structures; Section 14.5 describes the design of state machine classes, which encapsulate finite state machines; Section 14.6 describes the design of graphical user interaction classes, which hide details of the user interface; and Section 14.7 describes the design of business logic classes, which encapsulate business rules.