Package and Object diagrams
To simplify complex class diagrams, you can group classes into
packages. A package is a collection of logically related UML
elements. The diagram below is a business model in which the
classes are grouped into packages.
Packages appear as rectangles with small tabs at the top. The
package name is on the tab or inside the rectangle. The dotted
arrows are dependencies. One package depends on another if changes
in the other could force changes in the first.
Object diagrams show instances instead of classes. They are useful
for explaining small pieces of the model with complicated relationships,
especially recursive relationships.
This small class diagram shows that a university Department can
contain lots of other Departments.
The object diagram below instantiates the class diagram, by
replacing it by a concrete example.
Each rectangle in the object diagram corresponds to a single
instance. Instance names are underlined in UML diagrams. Class or
instance names may be omitted from object diagrams as long as the
diagram meaning is still clear.