Legacy System Anti-Patterns and a Pattern-Oriented Migration Response

Mature information systems grow old disgracefully as successive waves of hacking result in accidental architectures which resist the reflection of on-going business process change. Such petrified systems are termed legacy systems. Legacy systems are simultaneously business assets and business liabilities. Their hard-won dependability and accurate reflection of tacit business knowledge prevents us from undertaking green-field development of replacement systems. Their resistance to the reflection of business process change prevents us from retaining them. Consequently, we are drawn in this paper to a controlled pattern-oriented legacy system migration strategy. Legacy systems exhibit six undesirable anti-patterns. A legacy system migration strategy must focus upon the controlled elimination of these anti-patterns by the step-wise application of six corresponding desirable patterns. Adherence to this migration strategy results in adaptive systems reflecting purposeful architectures open to the on-going reflection of business process change. Without such a strategy there is a very real danger that legacy system migration will occur all too literally. That is, the old legacy system will be migrated to a new legacy system albeit it one using the latest buzzword-compliant technology.