Goal-directed elaboration of requirements for a meeting scheduler: problems and lessons learnt

Recently a number of requirements engineer­ ing languages and methods have flourished that do not only address what questions but also why, who and when questions. The objective of this paper is twofold: (i) to assess the strengths and weaknesses of one of these meth­ odologies on a non-trivial benchmark, and (ii) to illustrate and discuss a number of challenging issues that need to be addressed for such methodologies to become effective in supporting real, complex requirements engineering tasks. The problem considered here is that of a distributed meet­ ing scheduler system; the methodology considered is the KAOS goal-directed language and method. The issues raised from this case study include goal identification, the "deidelization" of unachievable goals, the handling of interfering goals, the impact of early formal reasoning, the merits of early reuse of abstract descriptions and cate­ gories, requirements traceability and the need to link requirements to retractable assumptions. and the potential benefits of hybrid acquisition strategies.