The evolution and maintenance of software is a field where theory has always been ahead of practice. In particular, it’s notoriously hard to introduce functional changes and document these in a way that guarantees the integrity of the system.

This paper discusses a behavior engineering (BE) approach to definition, design, and documentation of functional changes, using as examples two real-life applications, a microwave oven and a satellite control system. BE is a formal approach that ultimately allows one to derive an implementation from a set of requirements. The behavior of the system is modeled through behavior trees, which function as finite state machines capturing the behavior associated with each component.

One of the major challenges of behavior engineering is the documentation of changes and software evolution. While agile methods document the changes (and exchanges) by developers, this paper proposes a formalized approach, by modifying a design behavior tree (devDBT) with change requirements, called an evolutionary DBT.

Practitioners interested in formal modeling of system behavior and change management will find this paper interesting, even though the cost and usability of the formalization of complex systems is still an open question.