Overview

One of the most important motivations in practice for the application of object technology and subsequently component-based software engineering techniques is that new applications can be created with significantly less effort than in traditional approaches by assembling the appropriate prefabricated parts. However, contemporary object and component technologies are still some way from realizing the vision of application assembly, in particular when qualityof-service (QoS) issues are considered. With traditional approaches, the bulk of system integration work is performed in a distinct environment, the development environment, giving engineers the opportunity to pre-check the compatibility of the various parts of their system. This ensures that the overall application is working correctly in terms of functionality, behavior, and quality-of-service.

In contrast, the late integration implied by the assembly of readily deployable components means there is little opportunity to validate the correct functional and non-functional properties of the resultant application before deployment in the runtime environment. Although component developers may adopt rigorous test methodologies for checking component behavior, and deliver fault-free units, there is no guarantee that an assembly of such units will abide by the overall qualitative criteria that are required for the resultant application. In fact, even totally fault-free individual components that perfectly fulfill their individual qualitative measures may cause failures in the overall system if the platform does not provide the right support, or if the other components violate the overall qualitative criteria. The ARIANE 5 disaster is an example.

Compilers, configuration tools, and behavioral built-in contract testing can help by...