ABSTRACT
Class diagrams are the central specification notation of UML and of UML-RSDS. This chapter describes how class diagrams can be defined in UML-RSDS and used to specify system data.
A class diagram specifies the data of a system (and possibly data external to a system which it needs to be aware of). The diagram is a graphical representation of:
Classes or entity types – such as Student or Lecturer in Fig. 3.1. These denote the collection of all student or lecturer instances currently existing in the system (perhaps stored as objects in a Java executable, or as rows in a database table, for example). Abstract classes do not have instances of their own, instead their instances actually belong to the concrete subclasses of the class, at the leaves of the inheritance hierarchy beneath it.
