When talking about aspects like functional safety, reliability or availability of technical systems, a crucial point is to clearly define, what we are talking about. Do we mean the components, the hardware, when we say “The system is unreliable.” or “We have 99.99% availability.” ?

“The system” is indeed made up of a lot of individual components – blue in this figure. But at the end of the day we’d like to have functionality, performance, not hardware. All components are only used and needed to implement the desired functions – yellow in the figure.

So we usually have given requirements on the functional level, but need individual items – with their own properties – to make these functions work. No more, no less. The procedure of doing that by selecting, combining, assembling components appropriatelyis what we usually call “Engineering” – the art of Engineering.

In the next post we are going to show the two inverse views within system engineering and safety engineering.