The traditional reliability theory assumes that a
system and its components may only experience one
of two possible states: working or failed. Thus, we
call it binary reliability theory. Under this
assumption, reliability as defined above is an
excellent measure of performance of systems. There
exist several methods for designing systems with
high reliability. These methods include using large
safety factors, reducing the complexity of the
system, increasing the reliability of constituent
components, using structural redundancy, and
practicing a planned maintenance and repair
schedule. A good deal of effort has been focused in
the field of optimal redundancy allocation (Tillman
et al. 1980).