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About this lesson
A network diagram is a project scheduling technique that shows the relationship between tasks by depicting project activities as a flowchart.
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Quick reference
Network Diagram
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.
Instructions
- 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.
Login to download- 00:05 Hi I'm Ray Sheen, I'd like to talk with you about one of my favorite project
- 00:08 scheduling techniques, the Network Diagram.
- 00:11 The Network Diagram, is a flow chart of the project activities.
- 00:17 It shows the schedule relationship between tasks.
- 00:20 We can see how tasks are connected and how they impact each other.
- 00:24 The Project Management Body of Knowledge, the PMBOK Guide,
- 00:27 defines a Project Schedule Network Diagram as a graphic representation
- 00:32 of the logical relationships among project schedule activities.
- 00:35 Each task is represented by a node.
- 00:38 They are connected by arrows showing the relationships between the tasks.
- 00:42 We can see for each tasks, what other tasks are predecessors, and
- 00:46 what are successors?
- 00:48 This creates a focus on the handoffs between tasks, the completion of one and
- 00:53 the start of the next.
- 00:54 We can follow the progress to be sure that the ball is not dropped.
- 00:58 There are several important uses of the Network Diagram.
- 01:01 First of all, our advanced schedule analytical techniques require a network
- 01:04 diagram, and I'll talk more about those techniques in another lesson.
- 01:09 Second, I find this to be the best tool for
- 01:12 tracking projects with high uncertainty in the project estimates.
- 01:16 We know what to do, but we don't know how long it will take.
- 01:18 Other project scheduling techniques like the Gantt Chart
- 01:21 require a precise duration estimate.
- 01:24 With the Network Diagram, I encourage everyone to complete their task
- 01:27 as fast as possible, and then hand things off to the next task.
- 01:31 The key to network diagrams are the arrows connecting the tasks called dependencies.
- 01:37 These dependencies show which tasks must be completed before the next
- 01:40 task can start.
- 01:42 There are three types of dependencies.
- 01:44 The mandatory dependency is a dependency that cannot be broken.
- 01:48 It is usually based upon some physical relationship between the tasks.
- 01:53 For instance, if I have a testing task,
- 01:55 I must first create the test samples before I can conduct the test.
- 01:59 Without test samples, it's impossible to conduct a test.
- 02:04 The next type of dependency is a discretionary dependency.
- 02:07 Now these can't be broken, but only by adding risk to the project.
- 02:11 In fact, many times the dependency was created in order to reduce risk.
- 02:16 Back to our test example.
- 02:18 We created dependency that says, the testers cannot do the setup to prepare for
- 02:22 the test, until the test plan is approved.
- 02:25 This reduces the risk that the test setup is wrong and must be redone.
- 02:29 However, if we consider the likelihood of not getting approval for the test plan
- 02:33 is low, and we need to accelerate the project because of delays in other tasks,
- 02:37 we can break that dependency and do the set up before the test plan is approved.
- 02:42 We won't start testing without the approval, that might be too risky.
- 02:45 But we can do the set up.
- 02:47 The third dependency is an external dependency.
- 02:50 Although, these dependencies are outside the control of the project leader,
- 02:53 they can be broken in exceptional cases by stakeholders.
- 02:57 Continue with our example.
- 02:58 We may have test samples in an approved test plan, but
- 03:01 a higher priority project is using the test facility.
- 03:04 And we're delayed for several weeks until they finish.
- 03:07 However, senior managers can step in and change the priorities to allow
- 03:12 us access to the test facility even though the other project isn't finished.
- 03:16 Understanding the nature of the dependency will enable the project team
- 03:20 to manage them.
- 03:22 Now, creating a network diagram is pretty easy.
- 03:25 First, we identify the dependencies for each task by asking
- 03:29 what does that task require to be done before it can be started?
- 03:33 Next, we arrange the tasks in their normal sequence based upon the dependencies just
- 03:37 identified.
- 03:38 Now, plot each of the dependencies between those tasks so
- 03:41 we can see the relationships.
- 03:43 Finally, look for loops and danglers.
- 03:46 Loops exist when there are several task that may repeat over and over again.
- 03:50 The problem with these project is knowing how the estimate the number of iterations
- 03:55 through the loop.
- 03:56 Do they repeat twice?
- 03:57 Three times?
- 03:58 Four times?
- 04:00 Place a counter on the loop and create a maximum number before it must stop and
- 04:04 be replanned by the core team.
- 04:06 Loops should also be tracked as project risks.
- 04:09 Danglers are tasks that either have no starting relationship or
- 04:12 finishing relationship.
- 04:14 The lack of relationship makes it unclear what the task is related to.
- 04:17 If there's no predecessor relationship,
- 04:20 the project team doesn't know when to initiate the task.
- 04:23 If there is no successor relationship, we must ask the question,
- 04:26 why are we even doing this work since no one needs it?
- 04:30 There are a few hints and tips associated with network diagrams.
- 04:33 First, use this technique to track the handoffs between tasks.
- 04:37 It's a great way of enabling team members to work together
- 04:40 to move the project forward.
- 04:42 I often use a network diagram for managing small projects with high uncertainty,
- 04:46 because it's so easy to understand and follow.
- 04:49 However, it does add extra work for the project manager who must translate that
- 04:53 network into a calendar-based milestone chart for communication with stakeholders.
- 04:57 Even on large projects, I have often created a summary level,
- 05:00 milestone or Gantt chart for reporting purposes.
- 05:02 But use the network diagram for each major deliverable or phase.
- 05:07 Finally, in times of crisis, it's often the best technique to use.
- 05:11 During crisis, it may be impossible to create precise estimates, but
- 05:15 the flow of activities can be set.
- 05:17 Use the Network Diagram to communicate your plan with both the team and
- 05:20 the stakeholders.
- 05:21 And then, if you get more resources to resolve the crisis,
- 05:25 you'll know how to put them to best use.
- 05:27 As I've said, I like to use the Network Diagram.
- 05:31 It's a great way to illustrate and
- 05:33 manage the flow of activities through the lifecycle of a project.
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