Today, information system evolution primarily consists of extending the information systems and migrate them to modern platforms. This book tackles the problem of understanding and adapting information systems based on the systems' data and their interdependencies. In this context several methods and tools have been proposed for a reengineering process. Since legacy systems have grown over years and lack sufficient documentation, reengineering is a complex and hard task. Tool supported reengineering approaches and processes reduce the complexity and risks during information system maintenance. Still, reengineering approaches and tools often tackle only specific system parts or dedicated maintenance aspects. The approach presented in this book overcomes these limitations by providing processes that combine tools for reengineering the data as well as the applications. The focus is to handle uncertain knowledge by sustaining human exploration and iteration during tool supported reengineering. In practice uncertain knowledge during reengineering plays a fundamental role but it is often neglected by exiting approaches due to idealistic assumptions.