3

Class Diagram

The class diagram is the most important and most widely used description of an Object Oriented system. It shows the static structure of the core classes that are used to build a system. The most relevant features (attributes and methods) of each class are provided in the class diagram, together with the optional indication of some of their properties (visibility, type, etc.). Moreover, the class diagram shows the relationships that hold among the classes in a system. This gives a static view of the structural connections that have been designed to allow communication and interaction among the classes. Thus, the class diagram provides a very informative summary of many design decisions about the system’s organization.

Recovery of the class diagram from the source code is a difficult task. The decision about what elements to show/hide profoundly affects the usability of the diagram. Moreover, interclass relationships carry semantic information that cannot be inferred just from the analysis of the code, being strongly dependent on the domain knowledge and on the design rationale.

A basic algorithm for the recovery of the class diagram can be obtained by a purely syntactic analysis of the source code, provided that a precise definition of the interclass relationships is given. For example, an association can be inferred when a class attribute stores a reference to another class. One problem of the basic algorithm for the recovery of the class diagram is that declared types are an approximation of the classes actually instantiated in a program, due to inheritance and interfaces. An OFG based algorithm can be defined to improve the accuracy of the class diagram extracted from the code, in presence of subclassing and interface implementation. Another problem of the basic algorithm is related to the usage of weakly typed containers. Associations determined from the types of the container declarations are in fact not meaningful, since they do not specify the type of the contained objects. It is possible to recover information about the contained objects by exploiting a flow analysis defined on the OFG.

The basic rules for the reverse engineering of the class diagram are given in Section 3.1. Accuracy of the associations in presence of inheritance and in-