Project schedule network diagram is a technique for determining and documenting the sequence of activities and interdependence between them. It shows the order in which the activities should be scheduled and executed. The way those activities are presented is usually called the Activity on Nodes (AON) meaning the activities are presented with nodes connected with arrows that show the dependencies and order or sequence. In order to construct a network diagram it is necessary to have a WBS (work breakdown structure) and bottom up estimates identifying how much time (effort) each activity in the WBS would require and based on that the network diagram demonstrates what is the earliest and the latest time a certain activity can start and finish depending on when the previous activity on which the current one is dependent will finish. Therefore, there are 4 types of dependencies.
Finish to finish (FF),
Finish to start (FS),
Start to start (SS), and
Start to finish (SF).
The benefits of creating network diagram is to allow a project manager to track progress of each element of the project and be able to share the status with other relevant stakeholders. It also allows to establish project workflows and track dependencies and potential blockers. Below is an image of a simplified version of a project network diagram where the boxes (nodes) are connected with arrows signaling the dependencies among the activities and their sequence. Using the network diagram can then reveal the critical path of the project which is the longest sequence of tasks that must be finished for the entire project to be complete. Tasks that aren’t on the critical path can be delayed without impacting the overall schedule, however if there is a delay in any of the activities in the critical path, the entire project will have a delay.
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