In project management, a “dummy activity” is used in the Program Evaluation and Review Technique (PERT) or Critical Path Method (CPM) diagram to demonstrate a dependency between two activities that isn’t tied to any actual work.
A dummy activity is usually depicted as a dashed line connecting two tasks. It indicates that a specific task cannot start until another one is completed, but unlike normal tasks, it requires no effort, resources, or time. It’s merely a placeholder in the schedule to ensure that dependencies are maintained correctly and that the sequence of activities makes logical sense.
For example, suppose there are three tasks in a project: Task A, Task B, and Task C. Task B and Task C can only start after Task A is completed. However, Task C also cannot start until Task B is complete. In this case, a dummy activity might be used to represent the dependency between Task B and Task C, indicating that the two tasks must occur in sequence.
It’s important to note that dummy activities are used sparingly and only when necessary to maintain the logical integrity of the project schedule. They are usually an artifact of the particular way the project is being scheduled, and may not be required if the schedule is arranged differently.
Example of a Dummy Activity
Let’s consider a simplified construction project to illustrate the use of a dummy activity.
The project consists of four tasks:
- Task A: Design the building
- Task B: Obtain building permits
- Task C: Purchase construction materials
- Task D: Construct the building
The dependencies are as follows:
- Task B (Obtain building permits) can only start after Task A (Design the building) is completed, because you can’t apply for permits without a completed design.
- Task C (Purchase construction materials) can also only start after Task A is completed, because you need the design to know what materials to purchase.
- Task D (Construct the building) can only start after Task B and Task C are both completed, because you need both the permits and the materials to begin construction.
However, suppose there’s also a rule that the construction materials can’t be purchased until after the building permits have been obtained. This is an additional dependency that isn’t represented in the initial task list.
This is where the dummy activity comes in. We can introduce a dummy activity between Task B and Task C to represent the rule that you can’t purchase materials until the permits have been obtained. This dummy activity doesn’t represent any actual work – it just illustrates the dependency between these two tasks.
So, in this case, the dummy activity serves to maintain the logical sequence of the project, ensuring that tasks are carried out in the correct order.