Formal Software Development in MAYA

The formal development of industrial-size software is an errorprone and therefore an evolutionary process. Verifying formal specifications usually reveals hidden errors causing the change of parts of the specification. Also adding new functionality will result in changes of the specification which always endangers the verification work already done. In this paper we describe the system Maya which maintains formal developments. The Maya-system supports an evolutionary formal development since it allows users to specify and verify developments in a structured manner, incorporates a uniform mechanism for verification inthe-large to exploit the structure of the specification, and maintains the verification work already done when changing the specification. Maya relies on development graphs as a uniform representation of structured specifications, which enables the use of various (structured) specification languages to formalize the software development. Moreover, Maya allows the integration of different theorem provers to deal with the actual proof obligations arising from the specification, i.e. to perform verification in-the-small.