Bi-directional safety analysis of product lines

As product-line engineering becomes more widespread, more safety-critical software product lines are being built. This paper describes a structured method for performing safety analysis on a software product line, building on standard product-line assets: product-line requirements, architecture, and scenarios. The safety-analysis method is bi-directional in that it combines a forward analysis (from failure modes to effects) with a backward analysis (from hazards to contributing causes). Safety-analysis results are converted to XML files to allow automated consistency checking between the forward and backward analysis results and to support reuse of the safety-analysis results throughout the product line. The paper demonstrates and evaluates the method on a safety-critical product-line subsystem, the Door Control System. Results show that the bi-directional safety-analysis method found both missing and incorrect software safety requirements. Some of the new safety requirements affected all the systems in the product line while others affected only some of the systems in the product line. The results demonstrate that the proposed method can handle the challenges to safety analysis posed by variations within a product line.