The Rigorous Object-Oriented Analysis (ROOA) method provides a systematic development process by proposing a set of rules to be followed during the analysis phase. ROOA takes a set of informal requirements and an object model and produces a formal object-oriented analysis model that acts as a requirements specification. The resulting formal model integrates the static, dynamic and functional properties of a system in contrast to other object-oriented analysis methods which are informal and produce three separate models that are difficult to integrate and keep consistent. The model is expressed in LOTOS and provides a precise and unambiguous specification of a system's requirements. As the specification obtained is executable, prototyping can be used to check the conformance of the specification against the original requirements and to detect inconsistencies, omissions and ambiguities early in the development process.