The package diagram is used to organize model elements into package-able elements and define dependencies between the packages and/or model elements within the package. The package defines a namespace for the package-able elements.
The model can be organized in multiple ways where each viewpoint shows a single aspect of the model e.g.:
•system hierarchy (by level)
•by diagram type (by domain)
•by viewpoints (IPT - integrated product team)
Viewpoints allow you to view the model in a different way, e.g. in an analysis view which shows multiple hierarchy levels, e.g. Enterprise, System, Logical design etc.