Chapter 3. Class and Object Diagrams

This chapter focuses on class and object diagrams, which depict the structure of a system in general and at a particular point in time, respectively. First, I introduce class and object diagrams and how they are used. Next, I discuss classes, objects, and their details for modeling the elements that make up a system. Then, I go over associations, links, and their details for modeling the relationships among the elements that make up a system. Finally, I discuss various other types of elements and relationships. Many details that were not fleshed out in Chapter 2 are more fully elaborated here, and throughout the chapter I include suggestions relating to class and object diagrams.

Class modeling is a specialized type of modeling concerned with the general structure of a system. Object modeling is a specialized type of modeling concerned with the structure of a system at a particular point in time. You usually apply class and object modeling during analysis and design activities to understand the requirements and determine how a system will satisfy its requirements. Object modeling is usually used in conjunction with class modeling to explore and refine class diagrams. Class and object modeling usually start after the requirements have matured enough (as determined by your system development process) and continue in parallel with interaction and collaboration modeling (Chapter 6) throughout the system development process, while focusing on the elements that make up the system and their relationships.

As an architecture-centric process focuses on the architecture of a system across iterations, it is important to understand what elements make up a system and how they are related to one another. Given that every project has limited resources, you can use this information to determine how best to develop a system. This allows architects, designers, and developers to consider technical trade-offs concerning the system, including which elements can be developed in parallel, which elements can be purchased rather than built, and which elements can be reused.