  Decision support system in Requirements engineering plays an important role
in software development life cycle. The relationship between functional and
non-functional requirements often plays a crucial role in resolving conflicts
or arriving at decisions in requirements engineering phase. Goal-Oriented
Requirements Engineering (GORE) methods make a good attempt of addressing these
aspects which are helpful in decision support. We propose a GORE method -
Integrating goals after prioritization and evaluation (IGAPE). The method is
semi-formal in nature thereby ensuring active stakeholder participation. In
this paper we elaborate the various steps of IGAPE method. The output of IGAPE
is then given as input to a decision support system which makes use of Analytic
Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to
Ideal Solution (TOPSIS). Integration of IGAPE with AHP and TOPSIS will clearly
provide a rationale for various decisions which are arrived at during the
requirements engineering phase. The method is illustrated for an e-commerce
application and is validated by expert analysis approach.
