Software evolution: a requirements engineering approach

This thesis examines the issue of software evolution from a Requirements Engineering perspective. This perspective is founded on the premise that software evolution is best managed with reference to the requirements of a given software system. In particular, I follow the Requirements Problem approach to software development: the problem of developing software can be characterized as finding a specification that satisfies user requirements, subject to domain constraints. To enable this, I propose a shift from treating requirements as artifacts to treating requirements as design knowledge, embedded in knowledge bases. Most requirements today, when they exist in tangible form at all, are static objects. Such artifacts are quickly out of date and difficult to update. Instead, I propose that requirements be maintained in a knowledge base which supports knowledge-level operations for asserting new knowledge and updating existing knowledge. Consistency checks and entailment of new specifications is done automatically by answering simple queries. Maintaining a requirements knowledge base in parallel with running code means that changes precipitated by evolution are always addressed relative to the ultimate purpose of the system. This thesis begins with empirical studies which establish the nature of the requirements evolution problem. I use an extended case study of payment cards to motivate the following discussion. I begin at an abstract level, by introducing a requirements engineering knowledge base (REKB) using a functional specification. Since it is functional, the specifics of the implementation are left open. I then describe one implementation, using a reason-maintenance system, and show how this implementation can a) solve static requirements problems; b) help stakeholders bring requirements and implementation following a change in the requirements problem; c) propose paraconsistent reasoning to support inconsistency tolerance in the REKB. The end result of my work on the REKB is a tool and approach which can guide software developers and software maintainers in design and decision-making in the context of software evolution.