Validation Obligations: A Novel Approach to Check Compliance between Requirements and their Formal Specification

Traditionally, practitioners use formal methods pre-dominately for one half of the quality-assurance process: verification (do we build the software right?). The other half - validation (do we build the right software?) - has been given comparatively little attention. While verification is the core of refinement-based formal methods, where each new refinement step must preserve all properties of its abstract model, validation is usually postponed until the latest stages of the development, when models can be automatically executed. Thus mistakes in requirementsor in their interpretation are caught too late: usually at the endof the development process. In this paper, we present a novelapproach to check compliance between requirements and theirformal refinement-based specification during the earlier stages ofdevelopment. Our proposed approach - "validation obligations"- is based on the simple idea that both verification and validationare an integral part of all refinement steps of a system.