One of the main motivations for the reverse engineering of software programs is to help with software comprehension. Although several techniques have been presented in the literature to reverse-architect software, the corresponding views usually do not help much. In fact, most of the published techniques recover the architecture of the software by focusing on the abstract properties of the components such as coupling and coherence. We claim that the recovered components should rather represent abstract functional entities whose behavior could be understood independently from the others. Then, an abstract view of the system would represent the interactions between such functional entities. In this paper we present a technique and a tool able to generate abstract sequence diagrams to represent the global working of legacy programs. This shows the main interactions between abstract functional components. When comparing the automatically generated sequence diagrams to the one a developer would produce by hand, we realized that the representation were very close. Our work could then be considered as a first step to the automatic generation of human-understandable abstract views of the working of legacy programs.

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In program execution visualization, we wish to show where the action is unfolding when some high level use-case is played on the system. However, an important problem is to deal with the volume of data to display. One solution is to represent the architecture of the software in some familiar form. Then we proposed to represent it as a modern city, with buildings and districts, in a 3D space. In this paper we present the way the program execution is represented in such a space and we show how the understanding of this execution is facilitated. Since the display of the full execution trace is impossible because of its sheer size, we developed a trace segmentation technique. Then an information filter, called class omnipresence, is applied to further reduce the information to display. Finally, the resulting sequence of segments can be "played" on the screen, like in a movie.

In the context of reverse-engineering project we designed a usecase specification recovery technique for legacy information systems. With our technique, we can recover the alternative flows of each use-case of the system. It is based on a dynamic (i.e. runtime) analysis of the working of the system using execution traces. But "traditional" execution trace format do not contain enough information for this approach to work. Then we designed a new execution trace format together with the associated tool to get the program's dynamic decision tree corresponding to each of the use-case scenario. These trees are then processed to find the possible variants from the main scenario of each use-case. In this paper we first present our approach to the use-case specification recovery technique and the new trace format we designed. Then the decision tree compression technique is showed with a feasibility study. The contribution of the paper is our approach to the recovery of legacy systems' use-case, the new trace format and the decision tree processing technique.

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