Collaborative Development of System Architecture - a Tool for Coping with Inconsistency

Very large systems have an architecture that is designed to allow them to evolve through a long life. Such systems are developed by teams of architects. One of the first things the architects do is make a model of their architecture. This model constitutes the formal architecture description based on which software engineers will eventually build the real system. The architecture model is normally governed by a specialised metamodel whose rules determine the consistency and completeness of the description. The development of a system architecture is carried out cooperatively but independently by team members. Consequently it is quite normal for the architecture description as a whole to be both incomplete and inconsistent. The architects strive to eventually produce a complete overall (i.e. merged) description and to eliminate the inconsistencies. By means of an example, we show how and why the architecture model and the metamodel must co-evolve. We describe a design tool that we have developed to support this process of co-evolution. The tool allows a team of architects to detect inconsistencies in their separate and merged models. The tool tolerates inconsistencies. It produces reports of inconsistencies which then become targets for removal as the whole architecture description evolves.