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

Getting Started

If you are building a house, deciding where to place each room in relation to others is a critical task. At one level of abstraction, you might decide to put the master bedroom on the main level, away from the front of the house. You might next think through common scenarios to help you reason about the use of this room arrangement. For example, consider bringing in groceries from the garage. It wouldn't make sense to walk from the garage through your bedroom to get to the kitchen, so that's an arrangement you'd reject.

You can form a fairly complete picture of your house's floor plan just by thinking through these basic relationships and use cases. However, that's not enough. You can end up with some real flaws in your design if you don't consider more-complex relationships.

For example, you might like the arrangement of rooms on each floor, but rooms on different floors might interact in unforeseen ways. Suppose you place your teenager daughter's room right above your bedroom. Now, suppose your teenager decides to learn how to play the drums. You'd clearly want to reject that floor plan, too.

Similarly, you have to consider how underlying mechanisms in the house might interact with your floor plan. For example, you'll increase the cost of construction if you don't arrange your rooms so that you have common walls in which to run pipes and drains.

It's the same when you build software. Dependencies, generalizations, and associations are the most common relationships you'll encounter when modeling software-intensive systems. However, you need a number of advanced features of these relationships in order to capture the details of many systemsdetails that are important for you to consider so that you avoid real flaws in your design.

The UML provides a representation for a number of advanced properties, as Figure 10-1 shows. This notation permits you to visualize, specify, construct, and document webs of relationships to any level of detail you wish, even sufficient to support forward and reverse engineering of models and code.