Exploring early availability requirements using use case maps

Non-functional aspects including time constraints, distribution and fault tolerance are critical in the design and implementation of distributed real-time systems. As a result, it is well recognized that non-functional requirements should be considered at the earliest stages of system development life cycle. The ability to model non-functional properties (such as timing constraints, availability, performance, and security) at the system requirements level not only facilitates the task of moving towards real-time design, but ultimately supports the early detection of errors through automated validation and verification. In this paper, we introduce a novel approach to describe availability features in Use Case Maps (UCM) specifications. The proposed approach relies on a mapping of availability architectural tactics to UCM components. We illustrate the application of our approach using the In Service Software Upgrade (ISSU) feature on IP routers.