Chapter 1: Introduction to UML

As this example shows, there can be multiple Component diagrams for a system, depending on the number of subsystems or executables. Each subsystem is a package of components. In general, packages are collections of objects. In this case, packages are collections of components. The ATM example includes two packages: the ATM client and the ATM server. Packages will be discussed more in Chapter 3.

Component diagrams are used by whoever is responsible for compiling the system. The diagrams will tell this individual in what order the components need to be compiled. The diagrams will also show what run−time components will be created as a result of the compilation. Component diagrams show the mapping of classes to implementation components. These diagrams are also where code generation is initiated.

Deployment Diagrams

Deployment diagrams are the last type of diagram we will discuss. The Deployment diagram shows the physical layout of the network and where the various components will reside. In our ATM example, the ATM system comprises many subsystems running on separate physical devices, or nodes. The Deployment diagram for the ATM system is illustrated in Figure 1.17.

Figure 1.17: Deployment diagram for the ATM system

This Deployment diagram tells us much about the layout of the system. The ATM client executable will run on multiple ATMs located at different sites. The ATM client will communicate over a private network with the regional ATM server. The ATM server executable will run on the regional ATM server. The regional ATM server will, in turn, communicate over the local area network (LAN) with the banking database server running Oracle. Lastly, a printer is connected to the regional ATM server.

So, this one diagram shows us the physical setup for the system. Our ATM system will be following a three−tier architecture with one tier each for the database, regional server, and client.

The Deployment diagram is used by the project manager, users, architect, and deployment staff to understand the physical layout of the system and where the various subsystems will reside. This diagram helps the project manager communicate what the system will be like to the users. It also helps the staff responsible for deployment to plan their deployment efforts.

All of these diagrams together describe the system from several different perspectives. In Chapter 3, we will discuss each of these diagrams more closely and show how they are generated in Rational Rose. You will also be given the opportunity to try creating and using these diagrams in Rational Rose. But before we get into the

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