Claims, Arguments and Evidence (CAE)

Claims, Arguments and Evidence is a simple yet effective notation for presenting and communicating your safety argument.

Adelard developed CAE as a straightforward notation for structuring safety cases. It is one of the key notations available in ASCE.

A mind-map diagram showing how to structure safety cases

It allows you to structure your overall argument into the following elements:

Structure Description
Claim- a statement asserted within the argument that can be assessed to be true or false, e.g.
  • "System X is adequately safe during the shut down phase of operation"
  • "Unit testing is complete"
  • "All identified hazards are adequately managed in the hazard log"
  • "Design personnel are suitably qualified"
  • "Training materials have been reviewed"
Each claim is supported by a number of sub claims, arguments or evidence.

The claim may contain additional contextual material, for example explaining terms used and scope.

ASCE contains tools for editing rich narrative at any node in the safety case.

Argument- a description of the argument approach presented in support of a claim. e.g.:
  • "argue by considering safety of subsystems"
  • "because wiring conforms to relevant electrical standards"
This element is optional, but often it is good practice to include to explain the approach to satisfying the parent claim.

If the approach to supporting a claim is straightforward or well understood by the intended audience, it is permissible to simply link directly from the supporting claim.

Evidence- a reference to the evidence being presented in support of the claim or argument, e.g.
  • "the hardware reliability analysis report"
  • "interlock design documentation"
Usually the evidence node will summarise and link out to the relevant report containing the evidence.

ASCE contains a number of tools to support:

  • linking to, management and tracking of changes in the underlying evidence.