A package is a grouping of items. For Use Case diagramming, a package is used to represent a logical grouping of Use Cases, each describing a scenario in the system.

The package in itself does not generally contain much information; it acts as a packaging unit which contains Use Cases that describe a part of the system.

When you create a Use Case diagram in System Architect, you are required to specify the package that the Use Case diagram is contained in. All new classes and Use Cases that you draw on the diagram will belong to the specified package. You may move the Use Case diagram to another package, or move classes and Use Cases contained in the diagram to another package: see Moving UML definitions and diagrams between packages.

You may draw a package symbol on a Use Case diagram’s workspace. The package that you draw automatically becomes contained by the diagram's package, and is represented thusly in the browser. You may draw classifiers (classes and Use Cases) within a package symbol on a diagram to visually communicate that a class or Use Case belongs to a package -- however, simply drawing such classifiers within the package symbol does not create the semantic relationship in the repository that the contained symbols belong to the package. (To specify this semantically, you could create a 'child' Use Case or Class diagram for the package symbol, and draw Use Cases and classes on it; Use Cases and classes that you draw on the child diagram will belong to the package.)