Generation of multipurpose formal models from legacy code

Abstract

In this paper a method for generation of formal models from legacy systems code is proposed. The purpose of these models is to have a possibility of their application in different tasks such as automatic generation of executable tests, translation to modern programming languages, reverse engineering. The method pursues goals to decrease complexity of state space search and checking formulas satisfiability in relation to the direct code modeling, and to help legacy systems understanding and implementing in modern technologies. We focused on formalization of Cobol memory model as it is the most common language in legacy systems. Formal model is an attribute transition system with control flow. We proposed an algorithm for building enumerated types for any variables whose usage fulfills certain conditions, including translation procedure of numeric variables to enumerated ones. We considered a problem of translating non-comparable structures which overlap in memory (operator redefines in Cobol), are copied or compared with each other. In opposite to common approach of using union semantics (like union construction in C++), we described a method of structure fields decomposition which has no drawbacks of unions and makes for minimization of bytewise approach. We considered the developed method on the examples of structures as with simple fields as with arrays. We also gave examples of realization of bytewise approach in Java and C++ languages for those variables that cannot be represented as enumerated or numeric attributes. We tried this work for tests generation for middle-sized projects (up to 100 000 lines of code) where it showed efficiency of developed method, also generated formal models were used for debugging of Cobol to Java translator and business rules extraction.