Historically, software evolution appeared as an unexpected and
unplanned phenomenon that was observed in the original case
study [3]. Since that time, it gained steadily in importance and
moved into the center of attention of software engineers. There
were several recent summaries that mapped the field of software
evolution: Godfrey and German contrasted software evolution and
software maintenance, two terms that some authors incorrectly
interchange [4]. Mens and Demeyer edited a book that addresses
research issues in software evolution, reengineering, and so forth
[5]. This paper builds on these summaries including [2], maps the
present state of select software evolution themes, and outlines
their likely future directions.