Applicability of formal specification to maintenance of large-scale software

For over a decade, major research efforts have been devoted to formal specification techniques for system development. As a result, many specification languages and their support tools have been developed. But not much research has been done on the application of formal specifications to software maintenance. We developed a formal specification language called Waseda Specification Notation (WSN), and have been attempting to apply it to some existing large-scale software systems. One of these is the scheduler of the VM/SP operating system, which was completely specified in WSN. We tuned the scheduler on the basis of the formal specification described, and according to the current characteristics of our computer environment. This paper gives a detailed introduction to the benefits of applying formal specification methods during the maintenance of large systems. Experiences obtained during the study are also described.