Chapter 7 - Migration Strategies

Abstract

This chapter focuses on migration strategies. The central message of this chapter is to “Migrate Systems Incrementally.” In order to “Migrate Systems Incrementally,” a large number of other patterns should be considered the patterns that are considered to be most important for re-engineering object-oriented legacy systems are described in the chapter, with summarization of the main points. The central pattern of this cluster is “Migrate Systems Incrementally,” where the key motivation is provided by involving the users and building confidence. The first three fundamental patterns for minimizing risk and increasing the chances of success are “Involve the Users,” “Build Confidence,” and “Migrate Systems Incrementally.” It is very hard to “Migrate Systems Incrementally” unless the following practices are followed: (1) prototyping the target solution, (2) always having a running version, and (3) performing regression test after every change. Depending on the circumstances, there are various practices that may help to migrate systems incrementally that are making a bridge to the new town, presenting the right interface, distinguishing public from published interfaces, and deprecating obsolete interfaces. The following two practices may help to avoid making radical but unnecessary changes that are conserve familiarity and use profiler before optimizing: (1) “Conserving Familiarity” that warns against introducing radical interface changes, which may alienate users, and (2) using Profiler before optimizing that reminds to delay, considering performance issues until the existence of a problem can be demonstrated and the source of the problem can be pinpointed.