CAE building blocks (CAE Blocks) are a series of archetypal CAE fragments, derived from an empirical analysis of real cases in various domains. They are created using a standardised structure for combining CAE and are part of a stack of resources that we are developing to support authors of assurance cases. These resources comprise the basic concepts of claims, argument, evidence; building blocks with a set of specific CAE structures; templates created out of the blocks to address particular classes of problems, and the overall assurance case created using blocks and templates.
The block structure contains enhancements to the classical CAE approach. One enhancement is to how arguments are addressed: a special side-warrant element is introduced to explain and assist in a structured way whether the top-level claim can be deduced from the subclaims and under which circumstances the argument is valid. The five basic CAE building blocks that we have identified are:
• Decomposition – partitions some aspect of the claim.
• Substitution – refines a claim about an object into another claim about an equivalent object.
• Concretion – gives a more precise definition to some aspect of the claim.
• Calculation or proof – used when some value of the claim can be computed or proved.
• Evidence incorporation – incorporates evidence that directly supports the claim.
The CAE Blocks allow us to distinguish between deductive and inductive reasoning and between those aspects we can gain confidence from verifying models and those we need to validate with respect to the real-world.