A ship is comprised of a number of Systems; each system has a specific purpose and it can either operate alone or form a component part of a larger system. A System is a combination of interacting elements (human and/or machine) organized to achieve one or more stated purposes.
The usability of systems is described in terms of the efficiency, effectiveness and satisfaction of users performing tasks with the system in a defined context of use. This goal-based view of system performance offers considerable benefits in design.
The only real common concept seems to be safe. However, safe might not be given the same meaning by all users. Society would probably tend to view safe as no disasters while the crew would look at a safe ship as one that not only keeps floating but also is not inviting small personal accidents.
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