New approach to requirements trade-off analysis for complex systems

In this paper, we propose a faceted requirement classification scheme for analyzing heterogeneous requirements. The representation of vague requirements is based on Zadeh's canonical form in test-score semantics and an extension of the notion of soft conditions. The trade-off among vague requirements is analyzed by identifying the relationship between requirements, which could be either conflicting, irrelevant, cooperative, counterbalance, or independent. Parameterized aggregation operators, fuzzy and/or, are selected to combine individual requirements. An extended hierarchical aggregation structure is proposed to establish a four-level requirements hierarchy to facilitate requirements and criticalities aggregation through the fuzzy and/or. A compromise overall requirement can be obtained through the aggregation of individual requirements based on the requirements hierarchy. The proposed approach provides a framework for formally analyzing and modeling conflicts between requirements, and for users to better understand relationships among their requirements.