Complex sentence: It is sometimes assumed that the'S' in SIL refers to software but the failure rate of the software component of a system is merely a contribution to the overall SIL level of the system as a whole.
Split into simpler sentences: It is sometimes assumed that the'S' in SIL refers to software. However, the failure rate of the software component of a system is merely a contribution to the overall SIL of the system as a whole.