Junctions describe the flow logic of the process depicted in an IDEF3 process flow diagram.

In an IDEF3 Process Flow, a junction is a point where:

You can classify Junctions as fan-in or fan out. Multiple process paths terminate at a fan-in junction. Fan-in junctions represent the joining of a set of different process paths. Multiple process paths initiate at a fan out junction. Fan out junctions represent the splitting of a process into a set of alternative processing paths. When you draw line junctions, the system determines whether the junction is fan-in or fan out.

There are two types of junctions: asynchronous and synchronous. Asynchronous junctions are notated with one vertical line next to the left side of the junction box and synchronous junctions have vertical lines next to both sides of the junction box. Asynchronous fan-in junctions represent junctions where there are no timing constraints placed on the incoming process completions coming into the junction. Synchronous fan-in junctions represent junctions where the incoming processes must complete simultaneously (synchronously) before the UOB following the junction can be activated. Asynchronous fan out junctions represent junctions where there are no timing constraints on the starting of the UOBs following the junction. Synchronous fan out junctions represent junctions where the UOBs following the junction start simultaneously.