Chapter 3

Enterprises depend on business-critical systems that have been developed over the last three decades or more, also known as legacy systems. They have several well-known disadvantages (e.g., inflexible, domain unspecific, and hard to maintain), and this is recognized by both vendors and customers of these software systems. Both vendors and customers of these systems are well aware that better and more flexible customer specific solutions can be created following the service-oriented paradigm. Hence, mo-mentum is growing within enterprises to evolve legacy systems towards Service-Oriented Architecture (SOA). The evolution to SOA is favored because of various advantages including well established sets of open standards, platform and language independent interfaces, clear separation of service interface and implementation, and loose-coupling among services. In the last decade, there have been significant developments in legacy to SOA evolution, and that has resulted in a large research body of which there exists no comprehensive overview. This chapter pro-vides a historic overview, focusing on the methods and techniques used in legacy to SOA evolution. The authors conducted a systematic literature review to collect legacy to SOA evolution approaches reported from 2000 to August 2011. To this end, 121 primary studies were found and evaluated using an evaluation framework, which was developed from three evolution and modernization methods widely used in the software re-engineering domain. The evaluation constitutes the inventory of current research approaches and methods and techniques used in legacy to SOA evolution. The result of the SLR also identifies current research issues in legacy to SOA evolution and provides future research directions to address those research issues