Automatic verification of railway interlocking systems: a case study

Abstract: This paper presents experiences in applying formal verification to a large industrial piece of software. The area of application is railway interlocking systems which has earlier been addressed in for instance [9], [S], [7J, and [6’J. We try to prove requirements of the program controlling the Swedish railway station Alit&s by using the decision procedure which is based on the patented StUuarck algorithm. While some requirements are easily proved, others are virtually impossible to manage due to a very large potential state space, which is in excess of 10fOOOOO. We present what has been done in order to get, at least, an idea of whether or not such difficult requirements are fnlfilled or not, and we express thoughts on what is needed in order to be able to successfully verify large real-life systems.