The Unified Modeling Language User Guide SECOND EDITION [Electronic resources] نسخه متنی

Terms and Concepts

A class diagram is a diagram that shows a set of classes, interfaces, and collaborations and their relationships. Graphically, a class diagram is a collection of vertices and arcs.

Common Properties

A class diagram is just a special kind of diagram and shares the same common properties as do all other diagramsa name and graphical content that are a projection into a model. What distinguishes a class diagram from other kinds of diagrams is its particular content.

Contents

Class diagrams commonly contain the following things:

• Classes

• Interfaces

• Dependency, generalization, and association relationships

Like all other diagrams, class diagrams may contain notes and constraints.

Class diagrams may also contain packages or subsystems, both of which are used to group elements of your model into larger chunks. Sometimes you'll want to place instances in your class diagrams as well, especially when you want to visualize the (possibly dynamic) type of an instance.

Note

Component diagrams and deployment diagrams are similar to class diagrams, except that instead of containing classes they contain components and nodes, respectively.

Common Uses

You use class diagrams to model the static design view of a system. This view primarily supports the functional requirements of a systemthe services the system should provide to its end users.

When you model the static design view of a system, you'll typically use class diagrams in one of three ways.

1. To model the vocabulary of a system

Modeling the vocabulary of a system involves making a decision about which abstractions are a part of the system under consideration and which fall outside its boundaries. You use class diagrams to specify these abstractions and their responsibilities.

2. To model simple collaborations

A collaboration is a society of classes, interfaces, and other elements that work together to provide some cooperative behavior that's bigger than the sum of all the elements. For example, when you re modeling the semantics of a transaction in a distributed system, you can't just stare at a single class to understand what's going on. Rather, these semantics are carried out by a set of classes that work together. You use class diagrams to visualize and specify this set of classes and their relationships.

3. To model a logical database schema

Persistence is discussed in Chapter 24; modeling physical databases is discussed in Chapter 30 .