UML 2.0 in a Nutshell

Visibility

A package may specify visibility information for owned and imported elements, however elements may have only one of two levels of visibility: public or private. Public visibility means the element may be used outside the package (scoped by the package name). Private visibility means the element may be used only by other elements of the same package. Private visibility is useful for marking utility classes that help implement a subsystem or component you don't want to expose to the rest of the system.

You show public visibility by placing a plus sign before the element name. You show private visibility using a minus sign. Figure 3-4 shows the Utility package with some private helper classes.

Figure 3-4. The Utilities package with public and private members