Representing NFRs and FRs: A goal-oriented and use case driven approach

As software systems become more complex and important for business and everyday life, the need to better address non-functional requirements (NFRs) become increasing more crucial. However, UML and particularly the use case modeling-the current de facto standard method for functional requirements elicitation and modeling-lacks equally matured modeling constructs for dealing with NFRs. This paper proposes a framework for representing and integrating NFRs with FRs in the use case model at four association points: subject (system boundary), actor, use case, and communicate association. The NFRs can be implicitly associated with other related use case model elements based on the NFR propagation rules proposed to eliminate the need for redundant NFR specifications. A process is presented to demonstrate how to apply this framework, along with an illustration based on a simplified pricing system.