An Approach of Creating Component Design Specification for Safety-Related Software in Railway

This paper presents a practicable approach of creating component design specifications for safety related software used in railway industry. This approach, which is limited on software component level, claims that the traditional paper versions of software component design specifications now exist in the form of source code files. Firstly, this approach maps each software component to its source code files. With support from SVN tool, it content-wisely baselines certain specific versions of source code files as the starting points of software component design specification, with checking the comments written in the source code files. Then a detailed checklist based on the relevant mandatory clauses from EN 50128 [1] or EN 50657 [2] is used to review those baselined source code files, by filling a document named software component design specification review report. Evidences showing the fulfillment to each check item is documented and verified, which ensures the compliance to EN 50128 [1] or EN 50657 [2]. In case there is any non-fulfillment, corresponding actions shall be made for mitigation. If the source code needs update afterwards, it might cause the update of software component design specification, meaning to walkthrough another specific versions of source code files and update the software component design specification review report again. The presented approach has been successful applied in an actual railway SIL 2 electronic product development project and got a positive assessment result from the 3rd party assessor. It could save time and cost for software development project comparing to the ordinary approach, while still compliant with EN 50128 [1] or EN 50657 [2] for software with safety integrity level from 1 to 4.