Safety Goals and sub-Safety goals cohabitation to have related Goals

medini_1053080245

Dear all,

I have a question about Safety Goals, requirements and getting relation (related Goals).

My item is a system of sub-systems, where I want to define Safety goals (for the system) and sub Safety goals (for the Sub-systems). 

• Case 1: Using direct relation like the figure below it works fine. I can directly get the related Safety Goal of the [SR005] and get the upper System Safety Goal associated to [G006] and [G007] by using script: self.sourceRelations.target

 

• But the diagram I use to defined are more complex than the above example and I need to add intermediate "element" to make easier the understanding. I use to implement "false" Safety requirements with an additional column "N/A" to filter these requirements from the applicable one. --> it works fine when I have only requirements

• But when I want to do the same with sub Safety Goals (e.g. link [G007] to [NA009] as for grouping requirements+safety goal to make easier the understanding), it does not work, since a safety goal cannot contribute to a requirement (only a requirement can contribute to a Safety Goal).

So my question is very simple, how can I deal with two level of Safety Goals combined with intermediate "element/gate/???" to make easier the understanding of complex Safety diagram?

I need help please;-)

medini_1033829014

Dear Romain,

First of all, if compliance with ISO 26262 is mandatory for you, you should think twice before you do such a thing. ISO 26262-1 Clause 3.139 defines a Safety Goal as a "top-level safety (3.132) requirement as a result of the hazard analysis and risk assessment (3.76) at the vehicle level". In other words: if the Safety Goal is not on top level anymore, then it is just a Safety Requirement. Of course you can interpret the standard more freely, but when implementing medini we were aiming at standard compliance, so we did not consider this special case.

Then, there is perhaps the option to use Safety Goals (instead of requirements) for grouping, at least if below you plan to have further safety goals (goals under requirements really looks a little excptional to me). You could, for instance, have a structure tree like this:

If you still insist to have goals below requirements, the only relation that works would be the trace, which works for all pairings of objects in medini:

I would not model this way, honestly.

One case example that could make sense to me would be that a sub-requirements by System A is not satisfied locally (by some implementation in System A), but "remotely" by a Safety Goal of another system B. Imagine that you have an emergency brake function. False braking, when the road is slippery, could even lead to loss of control of the vehicle. But you have an ABS system that is made to prevent this. Then you can refer to the "remote Safety Goal" by a trace, but still have a requirement representing it in System A. For instance like this:

Is this sort of what you wanted?

Best regards

Bernhard