![]() ![]() The SEJ Software Development Risk Taxonomy focuses on general software development issues. ![]() When software safety requirements are imposed on legacy safety-critical systems, retrospective safety cases need to be formulated as part of recertifying the systems for further use and risks must be documented and managed to give confidence for reusing the systems. ![]() Product Engineering Class in the Software Safety Risk Taxonomy for Building Safety-Critical Systems c) Problems occur when trying to meet safety standards, and thus make retrospective safety cases, in legacy safety-critical computer systems. b) Evidence is gathered on the integrity of the system and put forward as an argued case. Safety Cases: a) Documented demonstration that a system complies with the specified safety requirements. NASA programs/projects will have their own set of safety requirements derived from the standard. Address the system perspective and some cover just software in the system > NASA-STD-8719.13B Software Safety Standard is the current standard of interest. Process-Oriented requirements are software engineering and safety management process requirements. Technical requirements are those such as "must work" and "must not work" functions in the system. Safety Standards contain technical and process-oriented safety requirements. So what can be done if the requisite documents for establishing and maintaining safety requirements traceability are not available? Safety standards often specify that software development documentation include process-oriented and technical safety requirements, and also require that system and software safety analyses are performed supporting technical safety requirements implementation. On the other hand, there are instances where safety standards are levied on legacy safety critical systems, some of which may be considered for reuse for new applications. ![]() How can traceability of software safety requirements be created for legacy safety critical systems? Requirements in safety standards are imposed most times during contract negotiations. Traceability of Software Safety Requirements in Legacy Safety Critical Systems It relies upon the NASA Software Safety Standard, risk assessment methods based upon the Taxonomy- Based Questionnaire, and the application of reverse engineering CASE tools to produce original design documents for legacy systems. This paper proposes a method for ascertaining formally, a software safety risk assessment, that provides measurements for software safety for legacy systems which may or may not have a suite of software engineering documentation that is now normally required. When process-oriented software safety requirements are levied on a legacy system after the fact, where software development artifacts don't exist or are incomplete, the question becomes 'how can this be done?' The risks associated with only meeting certain software safety requirements in a legacy safety-critical computer system must be addressed should such systems be selected as candidates for reuse. For legacy safety-critical computer systems, software safety requirements may not have been formally specified during development. Safety-critical computer systems must be engineered to meet system and software safety requirements. Software Safety Risk in Legacy Safety-Critical Computer Systems ![]()
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