Rule-Based Behaviour Engineering: Integrated, Intuitive Formal Rule Modelling

Requirement engineering is a difficult task which has a critical impact on software quality. Errors related to requirements are considered the most expensive types of software errors. They are the major cause of project delays and cost overruns. Software developers need to cooperate with multiple stakeholders with different backgrounds and concerns. The developers need to investigate an unfamiliar problem space and make the transition from the informal problem space to the formal solution space. The requirement engineering process should use systematic methods which are constructive, incremental, and rigorous. The methods also need to be easy to use and understand so that they can be used for communication among different stakeholders. Is it possible to invent a human intuitive modelling methodology which systematically translates the informal requirements into a formally defined model? Behaviour Engineering has arguably solved many problems. However, the size and low level of the final Behavior Tree makes it hard to match with the original requirements. Here, we propose a new requirement modelling approach called Rule-Based Behaviour Engineering. We separate two concerns, rules and procedural behaviours, right at the beginning of the requirement modelling process. We combine the Behavior Tree notation for procedural behaviour modelling with a non-monotonic logic called Clausal Defeasible Logic for rule modelling. In a systematic way, the target model is constructed incrementally in four well-defined steps. Both the representations of rules and procedural flows are humanly readable and intuitive. The result is an effective mechanism for formally modelling requirements, detecting requirement defects, and providing a set of tools for communication among stakeholders.