The Proteus Project Design Rationale and PPIS by Simon Monk, Univ. of Lancaster Design rationale is the reasoning behind design decisions.
Design rationale starts with a design question, that is a problem that needs to be solved.
There is usually more than one possible solution to the problem and these are enumerated. In addition the problem is often decomposed into a number of sub-goals that the proposed solutions should attempt to satisfy. There is now considerable interest in capturing the design rationale while a design is in progress and various tools have been developed that allow design rationale to be recorded. These tools are in general tied to a specific design rationale notation. Since the main formalism used in representing design rationale is the node and arc diagram, the PPIS is ideally suited to implementing a system for recording design rationale.