A safety integrity level from 1 to 4 (or basic integrity) is allocated to each safety-related function of the electronic system on the basis of its tolerable functional failure rate, following EN 50126-2 clause 10, and applies to the function, not to the system as a whole; the SIL determines the depth of evidence in clauses 5 and 7, the independence of roles and the techniques and measures of Annex E; SILs are not allocated to non-electronic functions.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.