Source transformation in software engineering using the TXL transformation system

Many tasks in software engineering can be characterized as source to source transformations. Design recovery, software restructuring, forward engineering, language translation, platform migration and code reuse can all be understood as transformations from one source text to another. TXL, the Tree Transformation Language, is a programming language and rapid prototyping system specifically designed to support rule-based source to source transformation. Originally conceived as a tool for exploring programming language dialects, TXL has evolved into a general purpose source transformation system that has proven well suited to a wide range of software maintenance and reengineering tasks, including the design recovery, analysis and automated reprogramming of billions of lines of commercial Cobol, PL/I and RPG code for the Year 2000. In this paper we introduce the basic features of modern TXL and its use in a range of software engineering applications, with an emphasis on how each task can be achieved by source transformation. 1. Background Many tasks in software engineering and maintenance can be characterized as source to source transformations. Reverse engineering or design recovery [1] can be cast as a source transformation from the text of the legacy source code files to the text of a set of design facts. Software reengineering and restructuring [2] can be cast as a source transformation from the poorly structured original source code text to the better structured new source code. Forward engineering or metaprogramming [3], can be cast as a transformation from the source text of design documents and templates to the instantiated source code files. Platform translation and migration tasks are easily understood as transformations from the original source code files to new source code files in the new language or paradigm. And code reuse tasks can be implemented as a source transformation from existing, tested source code to generic reusable source code modules. While many other methods can be applied to various parts of these problems, at some point each of them must involve dealing with actual source text of some kind at each end of the process. In this short paper we describe our experiences with attempting to tighten the relationship between the source text artifacts at each end of the processes by experimenting with actually implementing these and other software engineering tasks using pure source text transformations in the TXL source transformation language [4,5]. The experience we report is a summary of the results of many different projects over …