In practice, there are many needs for program transformations and program restructuring like simple global changes in calling conventions, migrations to new language dialects, goto elimination, and control flow restructuring. Since these transformations will affect millions of lines of code, a factory-like approach, with minimal human intervention, is desired to achieve a cost-effective, high-quality, solution. Recall from Section 1.3, that we define a renovation factory as a collection of software tools that aim at the fully automatic renovation of legacy systems by organizing the renovation process as an assembly line of smaller, consecutive, renovation steps.
Legacy systems show a lot of variety regarding their overall architecture, programming languages used, database organization, error handling, calling conventions, and the like. Experience shows that each renovation project is unique and requires an extensively tailored approach. The generation and customization of renovation factories is therefore a major issue. In order to promote flexibility and reusability, renovation factories should be built-up from from individual tools that are as small and general as possible. Our approach is illustrated in Figure 3 and consists of four phases: