PRECISE Seminar: Modeling and Validating the Train Fare Calculation and Adjustment System Using VDM++

The Train Fare Calculation and Adjustment System (TFCAS), developed by the OMRON Corporation, is a large-scale and complex system that helps passengers buy tickets and adjust their train fare on the railways across Japan. In this paper we present the results and experiences gained in a collaborative research project between AIST and OMRON, in which VDM++ has been applied to formalize TFCAS's specifications and validate its consistency as well as reliability properties. An executable VDM++ model can be used to raise the level of the quality of the informal system specification, the efficiency of existing system test-suites, and the quality of real implementation. The application of VDM++ enables us to detect 32 erroneous issues in the original informal specification document. Moreover, we also show how the development process can be improved in a front-loading manner using the formal method VDM++.