Precise scenarios - a customer-friendly foundation for formal specifications

A formal specification is beyond the comprehension of the average software customer. As a result, the customer cannot provide useful feedback regarding its correctness and completeness. To address this problem, we suggest the formalism expert to work with the customer to create precise scenarios. A precise scenario describes an operation by its effects on the system state with only few simple Z concepts. The customer would find a concrete precise scenario easier to understand than its corresponding abstract schema. The Z expert derives schemas based on the precise scenarios. Precise scenarios affords user involvement that improves the odds of a formal specification fully capturing the user requirements

Requirements specification using concrete scenarios

The precision of formal specifications allows us to prove program correctness. Even if formal methods are not used throughout the software project, formalisation improves our understanding of the problem. Formal specifications are amenable to automated analysis and consistency checking. However using them is challenging. Customers do not understand formal notations. Specifiers have difficulty tackling large problems. Once systems are built, formal specifications quickly become outdated during software maintenance. A method of developing formal specifications using concrete scenarios is proposed to tackle the disadvantages just mentioned. A concrete scenario describes system behaviour with successive steps. The pre- and post-states of scenario steps are expressed with actual data rather than variables. Concrete scenarios are expressed in a natural language or formal notation. They increase customer involvement in the creation of formal specifications. Scenarios may be ranked by priorities allowing specifiers to focus on a small part of the system. Formal specifications are constructed incrementally. New requirements are also captured in concrete scenarios which guide the modification of formal specifications. On one hand, concrete scenarios assist the creation and maintenance of formal specifications. On the other hand, they facilitate program correctness proofs without using conventional formal specifications. This is achieved by adding implementation details to customer scenarios. The resulting developer scenarios, encapsulating decisions of data structures and algorithms, are generalised to operation schemas. With the implementation details, the schemas written in formal notations are programs rather than specifications.EThOS - Electronic Theses Online ServiceGBUnited Kingdo