Goal Modelling and Reasoning in Tropos

We overview on-going research on modelling and analyzing goals in requirements engineering. Specifically, we introduce and discuss a qualitative model for goals, which – among other things -can cope with qualitative relationships and inconsistencies among goals. We then present an axiomatization of the model and propose sound and complete algorithms for forward and backward reasoning. In particular, given a goal model and labels for some of its goal elements, forward reasoning focuses on how to propagate these labels forward, towards root goals. Backward reasoning, on the other hand, focuses on finding a label assignment for leaf nodes of a goal graph that collectively satisfy/deny all root goals. Assuming that the satisfaction/denial of any leaf goal requires some unit cost, we also address the problem of finding a minimum cost label assignment to leaf goals for satisfying/denying all root goals of a goal graph. Both problems are solved by reducing them to the problems of satisfiability (SAT) and minimum-cost satisfiability (minimum-cost SAT) for Boolean formulas. The proposed algorithms have been implemented and are available through a tool named the GR-tool. To illustrate the whole framework, we include a simple case study adopted from the literature where a goal model is built and then analyzed.

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