D-case uses GSN(Goal Structuring Notation) a graphical notation when creating safety cases.GSN mainly consists of the following nodes.Of these, external and monitor is an extension of GSN of D-Case.
1.GoalA claim that ought to be discussed regarding a specific system.For example,”the system is dependable” or ”the system meets appropriate safety levels” etc.
2.StrategyA strategy node is used to describe a method of discussion used to achieve a goal.This method entails that a goal is divided into separate subgoals and elaborate said subgoals.For example,In regard to the goal“ the system is safe”, you might want to discuss according to the hazards that have already been identified and resolved.To achieve this you might use a strategy node "argument over each identified hazard", and then a corresponding subgoal might be "system can withstand hazard x is a subgoal".
3.ContextThe information that is the premise when discussing strategy and goals.For example, operational environment, system scope or list of hazards that have been identified.
4.EvidenceIntended to finally support an elaborated goal.For example, The verification results of tests or techniques.
5.UndevelopedIndicates that there is no sufficient evidence or discussions to guarantee a goal.
6.MonitorEvidence that can be acquired from a system in operation.For example, an internet access log.D-case tools in conjunction with the system, helps to ensure dependability while using monitor.
7.ExternalA link to another system`s D-Case.Systems do not individually sustain dependability, systems mutually interact towards sustaining dependability.
Fig.5, using arrows illustrates how to connect nodes.
- A goal is decomposed via a strategy node.
- The leaves of D-Case is either evidence, monitor, external or undeveloped.
- Context node is connected to either a goal or a strategy.
- There are two types of arrows
- goal -> strategy, strategy -> goal, goal -> evidence, monitor, external connections or undeveloped.
- goal -> context, strategy -> context (white arrows)