Very large software systems: A service-oriented approach

A very large scale, multi-organizational software system has typically a very long development cycle. Requirements continue to evolve while the system is being built. This affects already completed components as well as those not yet started. As a result, different parts of the system are in various phases of the development life cycle. Simultaneously, some parts of the system are in maintenance, others are in development, and others are still in the requirements phase. This leads to problems from the component interface perspective because the evolving requirements can lead to changes in the way system components need to communicate. This paper explores using a service-oriented approach to designing very large software systems. Service-oriented architectures are an architectural style that promote, among other things, loosely coupled application components and discoverable interfaces. Conceptualizing a very large software system as an enterprise of interacting, yet loosely coupled applications can help mitigate risks associated with evolving requirements and interfaces. Traditional approaches, such as data dictionaries, interface standardization, and locking requirements down tight early only go so far. Designers cannot anticipate all possible future needs or user requirements. Large systems amplify this concern, because customer personnel may change during development. Furthermore, these tactics tend to produce brittle, inflexible system architectures.