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

Getting Started

When you build a house, at some point in the project you'll make an architectural decision about your building materials. Early on, it's sufficient to simply state wood, stone, or steel. That's a level of detail sufficient for you to move forward. The material you choose will be affected by the requirements of your projectsteel and concrete would be a good choice if you are building in an area susceptible to hurricanes, for example. As you move forward, the material you choose will affect your design decisions that followchoosing wood versus steel will affect the mass that can be supported, for example.

As your project continues, you'll have to refine these basic design decisions and add more detail sufficient for a structural engineer to validate the safety of the design and for a builder to proceed with construction. For example, you might have to specify not just wood, but wood of a certain grade that's been treated for resistance to insects.

It's the same when you build software. Early in a project, it's sufficient to say that you'll include a Customer class that carries out certain responsibilities. As you refine your architecture and move to construction, you'll have to decide on a structure for the class (its attributes) and a behavior (its operations) that are sufficient and necessary to carry out those responsibilities. Finally, as you evolve to the executable system, you'll need to model details, such as the visibility of individual attributes and operations, the concurrency semantics of the class as a whole and its individual operations, and the interfaces the class realizes.

The UML provides a representation for a number of advanced properties, as Figure 9-1 shows. This notation permits you to visualize, specify, construct, and document a class to any level of detail you wish, even sufficient to support forward and reverse engineering of models and code.