Team:UNebraska-Lincoln/Integrated Practices 2
Safety Cases Overview
What is a Safety Case?
A safety case is an architecture to structure the reasoning software engineers use to gain confidence that systems will work as expected. Safety cases are especially developed for safety-critical software systems, like software controlling avionics systems or nuclear power plants.
Safety cases are recognized as a powerful tool in software engineering. Safety cases have been used many places around the world, and have been used extensively in Europe for over a decade to document safety for safety-critical software systems. Predictability of a safety-critical software system is essential. By developing safety cases, unexpected defects and vulnerabilities can be uncovered prior to implementation of the software system where failures could have devastating consequences.
How are Safety Cases formed?
The structure of a safety case follows a hierarchy where a series of arguments complemented with evidence captures the reasons why a system is presumed to work as expected. The high-level goal is the top level of the safety case hierarchy. High-level claims are made and these claims are broken down into sub-claims, then finally supported by evidence when it seems like a natural transition from a claim to evidence. Argumentation strategies are identified throughout the safety case to help clarify the arguments. Context is also provided to claims when deemed necessary.
GSN Fundamentals
A graphical representation, called Goal Structuring Notation (GSN), has been developed by T.P. Kelly (University of York) to help follow the arguments within a safety case. GSN is laid out in a flowchart style. Standardized shapes have been determined to represent the different “building blocks” of safety cases. A rectangle represents the claims and sub-claims. Evidence is represented by a circle. Strategies are represented by a parallelogram. Context is represented by a rectangle with rounded edges.
For more inforomation on GSN go here.
The Goal Structuring Notation - A Safety Argument Notation T P Kelly, R A Weaver in Proceedings of the Dependable Systems and Networks 2004 Workshop on Assurance Cases, July 2004.
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