In order to permit analysis, all RBDs created in the software must conform to the following constraints:
A diagram must contain at least one block.
If a diagram contains more than one block, all blocks in the diagram must be connected.
Diagrams must contain a single starting block and a single ending block, as shown next.
If a diagram consists of only one block, that block represents both the starting and ending block. Junction blocks can be used as starting and/or ending blocks that possess no reliability characteristics.
Circular references, as shown below, are not allowed. There must be a clear path towards the end of the RBD and the RBD cannot loop back on itself.