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A network diagram is a project scheduling technique that shows the relationship between tasks by depicting project activities as a flowchart.
When to use
The network diagram is helpful when the task duration estimates are very uncertain. In those circumstances, it is especially difficult to set dates with the other project scheduling techniques, but the relationships can usually be set.
Another time to use network diagrams is when the project is required to conduct a quantitative schedule analysis with scheduling analytical techniques such as critical path analysis, PERT analysis, or critical chain. Each of those techniques require a network diagram to do the analysis.
- Identify dependencies for each WBS task
- Arrange the tasks in their normal sequence
- Plot each dependency between the tasks
- Check for loops and danglers
Loops can cause a project to go into a set of activities (the loop) and repeatedly cycle through them indefinitely. Put a counter on the loop with a maximum number of times to prevent this.
Danglers are tasks with no start or end dependency – the relationship of the task to the project goals is not clear. If there is not task end relationship – the task may not be needed and can be eliminated. If it is needed, relate it to the appropriate deliverable. If there is no task start relationship, there is no way to initiate that portion of the project. Relate the start to the project start or an external milestone that can act as a trigger.
Hints & tips
This technique is excellent for managing the handoffs between tasks.
If a project schedule is taking too long, some dependencies can be modified. Dependencies are divided in three categories: mandatory, discretionary, and external. Mandatory dependencies cannot be modified because of a physical relationship between the tasks. Discretionary dependencies can be modified, but that normally increases the risk to the project. External dependencies can be modified by stakeholders not on the project team who can change business priorities.
Network diagram definition: "A graphical representation of the logical relationship among the project schedule activities." PMBOK® Guide
This definition is taken from the Glossary of the Project Management Institute, A Guide to the Project Management Body of Knowledge, (PMBOK® Guide) – Sixth Edition, Project Management Institute, Inc., 2017.
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