Figure A.2 shows a few of the UML's features for modeling class relationships.
Figure A.2. Class relations. Various lines between classes indicate relationships between objects of the classes.
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 Sequence , for example, use a Vector variable that CollectionParser declares to hold collections of other parsers.
An asterisk ( * ) indicates that zero or more instances of an object of a class may be connected to objects of an associated class. For example, a Sequence object has a reference to zero or more Parser objects.
A multiplicity indicator, such as 0..1 , indicates how many connections may appear between objects. For example, a Parser object can have zero or one associated Assembler objects.