Diagrams are Views of the Safety Model

The Diametric Safety Case Manager (DSM) is first and foremost a modelling tool. Most work in the DSM is done using diagrams, but these diagrams are just a representation of an underlying model. An entity such as a Goal or a Hazard can appear on several diagrams, but these are all views of a single entity; if it is changed then all the diagrams where it appears will be updated.

You can extract tables from the model using Matrices, and create documents using Reports. These models can also show the extension data attached to each entity.

Goal Structuring Notation

GSN diagram showing the argument that train doors will open at a station.
Example GSN diagram

GSN is a graphical notation for representing complex arguments linked to evidence. Explicitly it represents the individual elements of any safety argument (requirements, claims, evidence and context) and more significantly the relationships that exist between these elements.

Bow-tie Diagrams

Bow tie diagram showing the hazard of the train door opening while under way.
Bow tie diagram: Train door open while under way.

Bow-tie diagrams are a notation for managing risks and hazards. A risk or a hazard has a main event that has potential causes and outcomes, denoted by Events linked through Threat Lines. Controls are added to each Threat Line to show how the risks are managed.

Causality Diagrams

Causal Diagram of movement sensor.
Causal diagram of train movement sensor

Where a more detailed engineering analysis of failure modes and mechanisms is required the DSM also provides a notation to directly link cause and effect using a state machine notation similar to petri-nets.  In the future we plan to add numerical modelling to this notation so that reliability figures can be extracted in a way similar to fault trees.