Link groups facilitate communication between and synchronization of phases during execution of the batch. The two unit procedures referenced by the procedure PRC_PAINT are started at the same time. However, two phases in different unit procedures need to be synchronized, as shown in the following figure.
Dumping color from the color tank needs to be synchronized with charging color to the blender. Phases that require synchronization must belong to a link group so that the Batch Executive knows which phases are allowed to communicate with each other. Potentially, request messages could be sent to the Batch Executive from numerous phases in different recipes; the link groups keep the Batch Executive from trying to match requests that are not intended for each other.
In addition, a phase that needs to communicate with another phase during production of a batch must let the Batch Executive know that it is to have a phase partner. We will, therefore, increase the number of phase partners (from 0 to 1) for the two phase classes that need to be in link groups so that those phases can be set up to communicate.