A chain of accountabilities in open systems based on assured entrustments

Accountability achievement is indispensable to dependability. When the acquirer entrusts the provider with a task, the provider owes not only the accomplishment of the task itself but also the accountability with respect to the accomplishment. We claim that there should be an explicitly described agreement with the scope of accountability and the procedure of the accounts for emergencies, in the same way as there should be an explicitly described agreement on system requirements as is widely accepted nowadays. This paper proposes a consensus building process for entrustments of tasks in system life cycles, and formalism for explicit description of accountability. Our consensus building process ensures that the acquirer of the system can obtain the required information from the provider whenever necessary. An entrustment of a task between the acquirer and the provider may occur recursively in various levels in system life cycles. We also discuss the accountability in the supply chain of entrustment. Our consensus building process and form for description of explicit accountability leads to a consistent system of accountability in the "DEOS Process," which has been proposed as an instance of system life cycle with the consideration of long term operation of open systems. As an example, a file server system is given which has been developed and is operating in practice according to our proposal.