Case Study: Extracting a resource model from an object-oriented legacy application

Many companies have invested in legacy applications and want to benefit from the interoperability that the architectural style Representational State Transfer (REST) offers without redeveloping their software. One of the crucial parts when adding a REST interface to an existing application is creating an appropriate resource model. Utilizing any available model of the legacy application can accelerate development significantly because existing domain knowledge, data, and business process implementations can be reused. Despite the maturity of the architectural style, there is still little record of creating a resource model from existing object-oriented applications. This article presents a lightweight modeling process: First we harvest an existing object model for resource candidates, afterwards the resulting model is enhanced incrementally until a suitable resource model emerges. The process is illustrated by a case study that highlights interesting challenges, such as a comprehensive domain model and long running processes, as well as pragmatic solutions for these challenges. The paper demonstrates that it is feasible to add a RESTful interface to a legacy application even in a process rich environment.