Network Diagram

Quick reference

• 00:04 Hi, I'm Ray Sheen.
• 00:05 I'd like to talk with you about one of my favorite project scheduling techniques,
• 00:09 the network diagram.
• 00:10 The network diagram is a flowchart of the project activities.
• 00:14 It shows the schedule relationship between tasks.
• 00:17 We can see how tasks are connected and can impact each other.
• 00:21 The Project Management Body of Knowledge, the PMBOK guide,
• 00:24 defines the project schedule network diagram as a graphical representation of
• 00:29 the logical relationships among the project schedule activities.
• 00:33 Each task is represented by a node.
• 00:36 They are connected by arrows showing the relationship between the tasks.
• 00:40 We can see for each task what other tasks our predecessors or successors.
• 00:45 This creates focus on the handoffs between tasks, the completion of one and
• 00:49 the start of the next.
• 00:51 We can follow the progress to be sure that the ball is not dropped.
• 00:55 There are several important uses of the network diagram.
• 00:58 First of all,
• 00:59 our advanced schedule analytic techniques require a network diagram.
• 01:03 I will talk more about these techniques in other lessons.
• 01:06 Second, I find this to be the best tool for
• 01:09 tracking projects with high uncertainty in the project estimates.
• 01:13 We know what to do, but we don't know how long it will take.
• 01:17 Other project scheduling techniques like the Gantt chart require precise duration
• 01:20 estimates.
• 01:21 With a network diagram, I encourage everyone to complete their task as
• 01:26 fast as possible and then handoff to the next task.
• 01:29 The key to the network diagram are the arrows connecting the tasks called
• 01:33 dependencies.
• 01:34 These dependencies show which tasks must be completed before the next task
• 01:39 can start.
• 01:40 There are three types of dependencies.
• 01:42 The mandatory dependency is a dependency that cannot be broken.
• 01:46 It's usually based upon some physical relationship between the tasks.
• 01:50 For instance, if I have a test task,
• 01:52 I must first create the test samples before I can conduct the test.
• 01:56 Without test samples, it's impossible to conduct tests.
• 02:00 The next type of dependency is a discretionary dependency.
• 02:04 These can be broken but only by adding risk.
• 02:07 In fact, many times, that dependency was created in order to reduce risk.
• 02:13 Back to our test example, we create a dependency that says the testers
• 02:17 cannot do that setup to prepare for the test until the test plan is approved.
• 02:22 This reduces the risk that the test setup is wrong and must be redone.
• 02:27 However, we consider the likelihood of getting rapid approval the test plan is
• 02:32 low and we need to accelerate the project because of delays on other tasks,
• 02:36 we can break that dependency and do the setup before the approval is received.
• 02:41 We won't start testing without the approval,
• 02:44 that might be too risky, but we can do the setup.
• 02:47 The third dependency is the external dependency.
• 02:50 Although these dependencies are outside the control of the project team,
• 02:55 they can be broken in exceptional cases by stakeholders.
• 02:59 Continuing with our example, we may have test samples and an approved test plan,
• 03:03 but a high priority project is using the test facility and we're delayed for
• 03:08 several weeks until they finish.
• 03:10 However, senior management can change the priority and
• 03:13 allow us access to the test facility even though the other project isn't finished.
• 03:18 Understanding the nature of the dependencies will enable the project team
• 03:22 to manage them.
• 03:23 Creating a network diagram is easy.
• 03:26 First we identify the dependencies for each task by asking what does that
• 03:31 task require to be done before it can be started.
• 03:34 Next we arranged the tasks in their normal sequence using
• 03:38 the dependencies just identified.
• 03:40 Now plot each of the dependencies between those tasks so
• 03:44 we can see the relationships.
• 03:46 Finally, look for loops and danglers.
• 03:49 Loops exist when there are several tasks that may repeat over and over again.
• 03:54 The problem with these in a project is knowing how to estimate the number of
• 03:58 iterations through the loop.
• 03:59 Do they repeat twice, three times, four times?
• 04:03 Place a counter on the loop and
• 04:05 create a maximum number before it must be stopped and replanned by the core team.
• 04:09 Loops should also be tracked as project risks.
• 04:13 Danglers are tasks that either have no start relationship or finish relationship.
• 04:19 The lack of relationships make it unclear what the task is related to.
• 04:23 If there is no predecessor relationship,
• 04:26 the project team doesn't know when to initiate the task.
• 04:29 If there is no successor relationship, we must ask the question,
• 04:33 why are we doing this work since no one needs it?
• 04:37 There are a few hints and tips associated with network diagrams.
• 04:41 First, use this technique to track handoffs between tasks.
• 04:45 It's a great way of enabling team members to work together to move
• 04:50 the project forward.
• 04:51 I often use the network diagram for managing small projects with high
• 04:55 uncertainty, because it's so easy to understand and follow.
• 04:59 However, it can add extra work for the project manager if they have to translate
• 05:04 that network into a calendar-based milestone chart for
• 05:07 communication with stakeholders.
• 05:09 Even on large projects, I've often created a summary level milestone or
• 05:13 Gantt chart for reporting purposes but use a network diagram for
• 05:17 each major deliverable or phase.
• 05:19 Finally, in times of crisis on a project, it's often the best technique to use.
• 05:24 During a crisis, it may be impossible to create a precise estimate, but
• 05:29 the flow of activities can be set.
• 05:31 Use the network diagram to communicate your plan to both the team and
• 05:34 stakeholders, and then if you get more resources to resolve the crisis,
• 05:39 you'll know how to best use them.
• 05:40 As I said, I like to use the network diagram.
• 05:43 It's a great way to illustrate and
• 05:45 manage the flow of activities through the lifecycle of the project.

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