How to Read a Network Diagram
For the uninitiated project manager, reading a network diagram can be challenging. A network diagram helps you visualize all aspects of a project that you need to monitor. Reading a network diagram is a snap if you apply these two rules:
Rule 1: After you finish an activity or reach a milestone, you can proceed to the next activity or milestone, as indicated by the arrow(s).
Rule 2: Before you can start an activity or reach a milestone, you must first complete all activities and reach all milestones with arrows pointing to the activity you want to start or the milestone you want to reach.
Practice putting these rules to action with the diagram, here.
According to Rule 1, from Start, you can proceed to work on either Activity 1 or 3, which means you can do either Activity 1 or Activity 3 by itself or both Activities 1 and 3 at the same time. In other words, these two activities are independent of each other.
You may also choose to do neither of the activities. Rule 1 is an allowing relationship, not a forcing relationship. In other words, you can work on any of the activities that the arrows from Start lead to, but you don’t have to work on any of them. For example, suppose a part of your plan includes two activities to build a device: receive parts and assemble parts. As soon as you receive the parts, you can start to assemble them; in fact, you can’t start to assemble them until you receive them. But after you receive all the parts you ordered, neither rule says you must start to assemble them immediately; you can assemble them if you want to, or you can wait.
Of course, if you wait, the completion of the assembly will be delayed. But that’s your choice.
According to Rule 2, you can start working on Activity 2 as soon as you complete Activity 1 because the arrow from Activity 1 is the only one leading to Activity 2. Rule 2, therefore, is a forcing (or requiring) relationship. If arrows from three activities led to Activity 2, you’d have to complete all three activities before starting Activity 2. (The diagram doesn’t indicate that you can start working on Activity 2 by completing only one or two of the three activities that lead to it.)