Chapter 7. Package Diagrams
Classes represent the basic form of structuring an object-oriented system. Although they are wonderfully useful, you need something more to structure large systems, which may have hundreds of classes.
A package is a grouping construct that allows you to take any construct in the UML and group its elements together into higher-level units. Its most common use is to group classes, and that’s the way I’m describing it here, but remember that you can use packages for every other bit of the UML as well.
In a UML model, each class is a member of a single package. Packages can also be members of other packages, so you are left with a hierarchic structure in which top-level packages get broken down into subpackages with their ...