Requirements recovery from legacy systems by analysing and modelling behaviour

For any re-engineering of the legacy system such as alteration, modification or complete rebuild, to understand the original requirements can be important and sometimes critical. The semiotic approach we present aims at recovering requirements by studying the legacy system's behaviour. Using this approach, the requirements recovery consists of investigation activities at three major stages with a set of techniques for analysis and representation. The approach guides the analysis to be conducted from a number of angles at certain levels of detail using various software engineering and semiotic techniques. These techniques enable one, for derivation of the requirements, to study a legacy system from perspectives of different stakeholders, from its interaction with the users in the business context, and from information contents and processes of system operations. A case study applying this approach to recover requirements for a university's multi-site library is presented.