At What Level of Granularity Should We be Componentizing for Software Reliability?

In component-based software systems (CBSSs), software designers need to decide about decomposition level (level of granularity) which involves component sizes and the number of components. In these systems, decomposition level is important due to its major impacts on reliability. However, the basis to choose the decomposition level of a CBSS has not been addressed adequately in the existing research. On the other hand, software system components may vary with respect to their criticalities to different failures. The knowledge about component failure criticalities are currently not incorporated in the architectural design decisions of these systems. As a result, these systems consider different failures equally and disregard the various severities of different failures. In this paper, we study the level of decomposition of CBSSs with respect to its impact on their reliabilities based on various component failure criticalities. We discuss the level of decomposition impacts on CBSS architectures with respect to the architectural attributes and component failure criticalities. We derive the reliability of these systems and show the level of decomposition impacts on these system reliabilities.