Quantitative Assessment for Software Safety Integrity Level Based on Optimal Software Release Policies with Risk Cost  
Author Shigeru Yamada


Co-Author(s) Yuki Fujita; Takahiro Nishikawa


Abstract Reliability and safety for hardware in computer systems have been sufficiently studied in recent years. On the other hand, a safety-related system including software has not been assured with the proper method of calculating the software safety integrity level (abbreviated as SIL) in the functional safety standards, which is currently determined only by the number of development methods applied to practical safetyrelated system (abbreviated as SRSs). In this paper, we discuss quantitative assessment for it by applying reliability measures based on software reliability growth models (abbreviated as SRGM’s) that have been widely and successfully applied to practical software quality management activities. Based on a nonhomogeneous Poisson process (abbreviated as NHPP), the plausible methods of calculating software SIL in the functional safety standard are proposed. Further, we discuss the quantitative method for assuring software safety integrity level based on the optimal release policies with the test cost during testing-environment and the risk cost after the software product will be released.


Keywords Functional Safety, Functional Safety Standards, IEC 61508, Software Safety Integrity Level (SIL), Software Reliability Growth Model (SRGM), Nonhomogeneous Poisson Process (NHPP), Software Reliability, Instantaneous/Cumulative MTBF, Optimal Release Policies, Risk Costs
    Article #:  20188
Proceedings of the 20th ISSAT International Conference on Reliability and Quality in Design
August 7-9, 2014 - Seattle, Washington, U.S.A.