The Role of Data in Safety-Related Railway Control Systems

摘要

In the production of a computer-based safetyrelatedsystem, it is common to partition thehardware and software elements into a systemarchitecture. The software part of such anarrangement will generally include both theinstructions that are executed by the processor(s),and the data that is used and produced by theseinstructions. In some cases, a large amount ofstatic or configuration data forms an essentialelement within the system and plays a vital rolein ensuring its correct operation. While data issubject to errors, experience shows that it is oftennot subjected to safety analysis techniques suchas hazard and risk analysis. Data is often treatedin a totally unstructured manner (often makingerror detection difficult) and very rarely is faulttolerance used to protect the system from dataerrors.To illustrate the role and importance of data insafety-related systems, this paper looks at thedata associated with a railway command andcontrol system. Such a system has a range ofsafety-related functions, and must also operate inthe context of other safety, protection andbusiness planning systems. The paper considerstypical data errors associated with the railwayenvironment and proposes the early definition ofa system data architecture, which will allow theapplication of safety analysis techniques such asHOZOP.