From English to Formal Specifications

Formal methods provide an approach in which design steps can be shown to satisfy a specification. However, if a formal specification is wrong, then although the design steps may satisfy the formal specification, they are unlikely to satisfy the requirements of the system. Since most users are unfamiliar with formal methods, requirements specifications are often written in English. Such requirements, expressed in English, are then somehow translated to formal specifications. This transition has some potential for introducing errors and inconsistencies. In this paper we propose an interactive approach to proceeding from an informal specification to a formal specification in a systematic manner. The approach uses research in the area of natural language understanding to analyse English specifications in order to detect ambiguities and to generate an entity relationship model. The entity relationship model is then used as a basis for producing VDM data types and the specifications of some common operations. We illustrate the effectiveness of our approach by applying it to the specification of part of a route planning database system.