CASE tools usually lack methodological assistance and PSEEs usually lack validation of development outputs. We have developed a framework, named RHODES, which is based on a process description language (PBOOL) that enables modeling constructive activities and products of processes. It uses both object-oriented techniques to favor extendibility and reuse of processes and formal approach concepts to validate the development. All mechanisms required to enact PBOOL processes and to handle real development requirements (choice of heuristics, loops back, work sharing, etc.) are described in the execution model as development operators. RHODES assistance consists in providing developers with heuristics to perform activities; in managing the identified activities and dynamically computing their dependencies; in using assertions for validating development outputs, detecting and solving inconsistencies and partially automating propagation of changes.