Reliability covers how rarely the product fails, how much of the time it is available, how it behaves when part of it fails, and how quickly it recovers. The draft gives it four measure families. The four families describe different mechanisms and they need different data. Faultlessness is about the absence of failure in operation or test. Availability is about the proportion of time the service is usable. Fault tolerance is about continuing to operate when a component fails. Recoverability is about restoring service and data after a failure. A programme that reports availability alone has said nothing about how the product behaves when something breaks, and a faultlessness count without an operating window cannot be compared. Reliability measures are the ones most often built from operational data, which means the observability of the product is part of the measurement method.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.