When a software system enters the maintenance phase, the availability of accurate and consistent information about its organization can help alleviate the difficulties of program understanding. Reverse engineering methods aim at extracting such kind of information directly from the code. While several tools support the recovery of the class diagram from object oriented code, no work has insofar attacked the problem of statically characterizing the behavior of an object oriented system by means of diagrams which represent the class instances (objects) and their mutual relationships. In this paper a novel static analysis algorithm is proposed for the extraction of the object diagram from the code, based on a program representation called the object flow graph. Partial object diagrams can be associated dynamically to the system by executing and tracing the program on a set of test cases. The complementary nature of these two views will be discussed, and a novel approach to object orien...