Detecting a loop condition

A current plan is made of one or more networks. A network is made of a number of operations that are linked to one another by some dependencies. Every network must contain at least one of the following operations:

First Operation (FOP): Operation with no predecessors. It is considered an entry point to the network.
Last Operation (LOP): Operation with no successors. It is considered an exit point from the network.

To detect a loop condition, batch daily planning programs perform two kinds of check on the network.

The first check performed by batch daily planning programs is to ensure that the network has at least one first and one last operation. If either or both of them are missing, a loop condition is detected and reported as NO ENTRY AND/OR EXIT POINT loop in the EQQMLOG and EQQLOOP data sets. For details about this type of loop, see "NO ENTRY AND/OR EXIT POINT" loop.

The second check performed by batch daily planning programs is to ensure that all the operations in the network can be assigned an earliest start time (EAS). When processing the network, batch daily planning programs create a current plan where all the operations are assigned a planned start time, to approximately indicate when each operation can run. If, at the end of this process, one or more operations are left with no EAS assigned, a loop condition is detected. This type of loop is reported as SOME NODES COULD NOT BE CHECKED in the EQQMLOG and EQQLOOP data sets. For details, see "SOME NODES COULD NOT BE CHECKED" loop.