Software Architect's Handbook

Issues with legacy applications

Working with a legacy application usually brings with it various problems that need to be overcome. This is a part of the challenge when working with a legacy system. Perhaps most importantly, a legacy application tends to be difficult to maintain and extend. It may use older, possibly outdated, technologies and it may not follow best practices for software development.

A legacy application tends to be older, and over the life of the project many different developers may make modifications to it. Software entropy, or disorder in a software system, increases over time. This concept comes from the Second Law of Thermodynamics, which states that the level of entropy either stays the same or increases but it does ...