Software engineering research has focused mainly on software construction and has neglected software maintenance and evolution. Proposed is a shift in research from synthesis to analysis. Reverse engineering is introduced as a possible solution to program understanding and software analysis. Presented is reverse engineering technology developed as part of the Rigi project. The Rigi approach involves the identification of software artifacts in the subject system and the aggregation of these artifacts to form more abstract architectural models. Reported are some analyses on the source code of SQL/DS, performed by the authors while visiting the Program Understanding project at the IBM Centre for Advanced Studies in Toronto.

The FermaT transformation system, based on research carried out over the last twelve years at Durham University and Software Migrations Ltd., is an industrial-strength formal transformation engine with many applications in program comprehension and language migration. This paper describes one application of the system: the migration of IBM 370 Assembler code to equivalent, maintainable C code. We present an example of using the tool to migrate a small, but complex, assembler module to C with no manual intervention required. We briefly discuss a mass migration exercise where 1,925 assembler modules were sucessfully migrated to C code. Keywords: Assembler, Migration, Comprehension, Formal Methods, WSL, Wide Spectrum Language, Program Transformation, Legacy Systems, Restructuring.

In this paper we consider a particular class of algorithms which present certain difficulties to formal verification. These are algorithms which use a single data structure for two or more purposes, which combine program control information with other data structures or which are developed as a combination of a basic idea with an implementation technique. Our approach is based on applying proven semantics-preserving transformation rules in a wide spectrum language. Starting with a set theoretical specification of "reachability" we are able to derive iterative and recursive graph marking algorithms using the "pointer switching" idea of Schorr and Waite. There have been several proofs of correctness of the Schorr-Waite algorithm, and a small number of transformational developments of the algorithm. The great advantage of our approach is that we can derive the algorithm from its specification using only general-purpose transformational rules: without the need for complicated induction arg...

A wide spectrum language is presented, which is designed to facilitate the proof of the correctness of refinements and transformations. Two different proof methods are introduced and used to prove some fundamental transformations, including a general induction rule (Lemma 3.9) which enables transformations of recursive and iterative programs to be proved by induction on their finite truncations. A theorem for proving the correctness of recursive implementations is presented (Theorem 3.21), which provides a method for introducing a loop, without requiring the user to provide a loop invariant. A powerful, general purpose, transformation for removing or introducing recursion is described and used in a case study (Section 5) in which we take a small, but highly complex, program and apply formal transformations in order to uncover an abstract specification of the behaviour of the program. The transformation theory supports a transformation system, called FermaT, in which the applicability conditions of each transformation (and hence the correctness of the result) are mechanically verified. These results together considerably simplify the construction of viable program transformation tools; practical consequences are briefly discussed.

In this paper we give a brief introduction to the foundations of WSL transformation theory and describe how the concept of program slicing can be formalised in the theory. This formalism naturally lends itself to several generalisations including amorphous slicing and conditioned slicing. One novel generalisation is "semantic slicing" which combines slicing and abstraction to a specification. Interprocedural semantic slicing has been implemented in the FermaT transformation system [16]: an industrial-strength transformation system designed for forward and reverse engineering, re-engineering and program comprehension.

There is a vast collection of operational software systems which are vitally important to their users, yet are becoming increasingly difficult to maintain, enhance and keep up to date with rapidly changing requirements. For many of these so called legacy systems the option of throwing the system away an re-writing it from scratch is not economically viable. Methods are therefore urgently required which enable these systems to evolve in a controlled manner. The approach described in this paper uses formal proven program transformations, which preserve or refine the semantics of a program while changing its form. These transformations are applied to restructure ans simplify the legacy systems and to extract higher-level representations. By using an appropriate sequence of transformations, the extracted representation is guaranteed to be equivalent to the code. The method is based on a formal wide spectrum language, called WSL, with accompanying formal method. Over the last ten years we h...

ion Martin Ward Computer Science Dept Science Labs South Rd Durham DH1 3LE April 9, 1996 Abstract What does it mean to say that one program is "more abstract" then another? What is "abstract" about an abstract data type? What is the difference between a "high-level" program and a "low-level" program? In this paper we attempt to answer these questions by formally defining an abstraction relation between programs which matches our intuitive ideas about abstraction. The relation is based on examining the operational semantics of the programs, expressed as a set of traces (sequences of states) from a given initial state to a possible final state. KEY WORDS: Abstraction, Software Maintenance, Transformations, Refinement, Transformational Programming 1 Introduction In discussing software development, refinement of specifications into programs, reverse engineering from programs into specifications, and other related areas, concepts such as "high-level program" verses "low-level program", ...

Software reengineering has been described as being "about as easy as reconstructing a pig from a sausage" [11]. But the development of program transformation theory, as embodied in the FermaT transformation system, has made this miraculous feat into a practical possibility. This paper describes the theory...

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A method is described for obtaining useful information from legacy code. The approach uses formal proven program transformations, which preserve or refine the semantics of a construct while changing its form. The applicability of a transformation in a particular syntactic context is checked before application. By using an appropriate sequence of transformations, the extracted representation is guaranteed to be equivalent to the code. In this paper, we focus on the results of using this approach in the reverse engineering of medium scale, industrial software, written mostly in languages such as assembler and JOVIAL. Results from both benchmark algorithms and heavily modified, geriatric software are summarised. It is concluded that the approach is viable, for self contained code, and that useful design information may be extracted from legacy systems at economic cost. We conclude that formal methods have an important practical role in the reverse engineering process.