Abstract
Fundamental mathematical expressions on system's safety are shown as followings:
(i) System's safety can be replaced by system's reliability with its suitable definition.
(ii) System's reliability can be represented as function of elements' reliabilities, of the system, though the function should be reduced according to the defintion of system's failure.
(iii) It is difficult to express human characteristics as system's elements mathematically. It is expected to study it fruitfully in this area.
(iv) Improvement of system's reliability is established by redundancies of system's construction and elements. There is a problem on optimal cost allocation.
(v) Optimal cost allocation problems can be solved by Dynamic Programming Method if system's construction and characteristics of system's elements (especially effective sensitivities and cost functions) are known.
