Figure A.2 shows a few of the UML's features for modeling class relationships.
In Figure A.2, note the following.
A diagram may show a class name or method name in italics to indicate that the class or method is abstract.
A large, open arrowhead points to a class's superclass.
A line between classes indicates that instances of the classes are connected in some way. Most commonly, a line on a class diagram means that one class has an instance variable that refers to the other class. The classes Alternation and ...