Kiyotoshi Komaya

An approach to specifying and verifying safety-critical systems with practical formal method SOFL

One of the primacy concerns in developing computer embedded safety-critical systems is how to develop quality software. Software must fulfill its functional requirements and must not contribute to the violation of safety properties of the entire system. To this end, capturing error free and satisfactory functional requirements is crucial before proceeding to the subsequent development phases. We describe an approach to specifying and verifying software for safety-critical systems with the practical formal method SOFL (Structured-Object-based-Formal Language). Requirements specification focuses on the functionality of the software, but with the consideration of safety constraints and its interaction with the surrounding operational environment. The verification of specifications can be carried out using three techniques: data flow reachability checking, specification, testing, and rigorous proofs, respectively. We apply this approach to a realistic railway crossing controller for a case study and analyzes its result.

Applying SOFL to specify a railway crossing controller for industry

This paper describes an application of the formal engineering method SOFL (Structured-Object-based-Formal Language) to specifying a realistic railway crossing controller for potential use in industry. As the railway crossing controller is a safety critical and real-time system, this application demonstrates the capability of SOFL for developing safety-critical and real-time systems and provides a foundation for implementing such a software controller in practice. It also shows that appropriate integration of structured methods with graphical notation, formal notation, and natural language offers a good readability and traceability as well as an effective mechanism for reducing complexity of systems.

A feasibility study of train automatic stop control using range sensors

Automatic train control plays a key role in improving the efficiency and safety of train movements, as well as the riding comfort of passengers. In Japan, train control systems have been successfully implemented since 1980s. These systems are required to control the train position and speed as accurately as possible. This is mostly dependent on the axle generators and transponders. More specifically, the axle generators measure the speed and moving distance from the reference points specified by the transponders. However, the train control systems using these devices still fail to achieve a correct train position, due to skidding or slipping, until passing over reference points. This paper focuses on the train automatic stop control (TASC), and presents a new TASC system using a commercial range sensor instead of transponders so that the train equiped with the system can detect its position continuously.

Revised design calculations of elevator systems

For sufficient carrying capacity and passenger comfort and convenience, it is very important to design suitable elevator systems (e.g., the appropriate number of cages, velocity, capacity, etc.) using models that describe real elevator movements. The procedure used in conventional design calculations for office buildings is to determine the carrying capacity for peak traffic situations using simple passenger arrival models. The paper presents new revised design calculations using the balanced traffic model, which can deal with elevator movements considering the passenger arrival rate. As some performance indices to evaluate the quality of service can be calculated using this model, elevator system designers can now determine appropriate elevator facilities satisfying goals. The validity of the proposed model is also shown by comparison with measured data for real elevator systems.

A combined approach of microscopic and macroscopic simulation for rail traffic

The paper presents a combined approach of rail traffic simulation using suitable models, both microscopic and macroscopic. In rail traffic, train motions do not depend directly on preceding train motions, as in road traffic, but only on the speed limit in the current block section. Using the history of the speed limit in each block section, simulation of the movement of individual trains between stations can be performed independently. Based on this fact, we have formed a new microscopic model and proposed a combined approach, applying the macroscopic model to normal train runs and the microscopic model to othes. Our combined approach makes it possible to obtain quick responses by macroscopic simulation and detailed results by microscopic simulation.