Main assumptions and mathematical bases for BDFs
Reliability block diagrams

From a mathematical point of view, a BDF is an acyclic directed graph, i.e. it has one input and one output, and no loops or feedback. It is based on the following fundamental assumptions:

• 1) the system has only two states (e.g. on/off);

• 2) blocks have only two states (e.g. on/off);

• 3) the BDF represents the logic function linking the operating state of the system to the operating states of its blocks;

• 4) the blocks are independent of each other.

The two states of the blocks or system can also be referred to as success/failure, working/failed, available/unavailable, etc. When the above assumptions are met, calculations...