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Sequencing & Dependencies

Sequencing & Dependencies

Author: Jeff Carroll

This lesson provides an overview for determining the work required to complete a project.

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Source: Image of schedule, Public Domain,; Image of bridge, Public Domain,; Image of road, Public Domain,; Image of chart, arrow, Public Domain, Images by Video Scribe, License held by Jeff Carroll.

Video Transcription

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Hi, I'm Jeff. In this lesson, we'll learn about sequencing and dependencies. To create a schedule, the project manager must put the task from the WBS into sequences. However, due to dependencies and other issues, tasks may not proceed smoothly one after the other. And that's what we'll discuss today.

For each activity in the WBS, the project manager should attempt to place the activity, and the tasks under the activity, into logical sequences. In other words, if a task must be completed before another task, then it will be first in the sequence. For example, you must build the supports in a bridge before you place the road work down.

Not all tasks will have a logical sequence though. Some tasks are not reliant on other work, so these tasks can be done at the same time other work is happening assuming the proper resources are available. Often, when the project manager is sequencing tasks, new tasks are defined or tasks are broken down into smaller tasks. As this occurs, the project manager will need to update the WBS with the changes.

When tasks have a logical sequence, it is said that one task is dependent on another. It is critical for the project manager to identify the dependencies in a project schedule as issues with dependencies are a primary cause of schedule slippage. Remember that tasks without dependencies can be done in parallel with other tasks as long as the resources are available to complete all the work at the same time.

Determining all dependencies might require the project manager to make a number of review passes through the schedule. Once all dependencies have been found, it's the project manager's responsibility to document the dependencies along with their associated tasks and activities. When documenting activities, tasks, and dependencies, it's typical to number them based on this scheme.

Use whole numbers for activities, such as 1.0, 2.0, and 3.0, until all activities in a project have been numbered sequentially. Each task under an activity is then numbered with the activities number. Then, the value after the decimal point is changed based on the order the work will proceed. For example, the tasks under activity 2.0 would be number 2.1, 2.2, 2.3, and so on. If a task order changes be sure to update the number to reflect the change in sequence.

Now, let's discuss the ways the dependencies can impact the timing between tasks. Lag time and lead time are two important concepts a project manager should consider when working with a schedule. Lag time is the time delay between two tasks, and these are either caused by an issue with dependencies or an issue with the resources allocated for the task. For example, if one task is complete, but the next task must wait two days until a resource is done with other work, that's considered lag time.

A more complex situation might involve tasks that have multiple dependencies. For example, imagine your building a chair. The legs must be complete and the seat must be complete before the chair can be assembled. However, if the legs are done in three days, and the seat is done in five days, the assembly of the chair must wait five days before it can start. That means there is lag time between the leg creation and the chair assembly. Lag times can lead to resources sitting on their hands while they wait on other work to be done, and it is inefficient for a project.

Lead times indicate when a second task can start once a previous task is only partially complete. For example, a new road only needs to be partially complete before other workers can start painting the traffic lines. Once all of these details are worked out by the project manager, then the project schedule should reflect the overall project time. This is the time from the start date of the project to the end date when all tasks are complete and all deliverables are done. That's why it's important for a project manager to understand dependencies, lag time, and lead time because they have a significant impact on the projects total time.

And that's all for this lesson. Good job! You should now understand how to sequence activities and tasks, what dependencies are and how they impact the timeline, how to document activities and tasks, when lag time and lead time will occur, and how all of this affects the project's total time to completion. Thanks, and have a great day.

Terms to Know

Logical relationships between activities and between tasks.

Lag Time

The time delay between two tasks within a project schedule.

Lead Time

The time required before a successor task can begin.