KAOS is a methodology for requirements engineering enabling analysts to build requirements models based on the successive refinement of system goals and the assignment of responsibilities of agent types to requirements. It also allows the definition of obstacles and provides facilities to operationalise the requirements.

More information and papers about KAOS can be found here. A tutorial on KAOS that uses Objectiver can be found under KAOS Tutorial. Objectiver is a commercial tool to create KAOS requirements models.

While current versions of KAOS focus on graphical modelling of system goals and requirements, the original focus was on the formalisation and operationalisation of these elements.

Bibliography:

• Anne Dardenne, Axel Van Lamsweerde, and Stephen Fickas. "Goal-directed requirements acquisition." Science of Computer Programming, vol. 20(1-2), pp. 3-50, 1993. DOI
• Axel van Lamsweerde, and Emmanuel Letier. "From object orientation to goal orientation: A paradigm shift for requirements engineering." Radical Innovations of Software and Systems Engineering in the Future. Lecture Notes in Computer Science, vol. 2941, pp. 325–340, M. Wirsing, A. Knapp, and S. Balsamo, Eds. Springer Berlin Heidelberg, 2004. pp. 325-340. DOI