Having many challenging responsibilities involved in project management, possessing the right tools to assist in the successful execution of tasks becomes critical.
What is the precedence diagram method?
The precedence diagram method is a charting technique that is used to develop a network diagram of the project schedule and uses so-called “nodes” to represent activities.
These nodes are connected through arrows to represent a sequential progression of dependencies between activities in the plan.
How to create the precedence diagram
To create a precedence diagram and thus to establish the dependency relationships between tasks, the first stage of planning is to focus on the work breakdown structure.
The whole project becomes more convenient and manageable when the various tasks are broken down into smaller parts.
At this stage you will have a table with three columns, the first column listing the tasks and the second with their sequence, while the third will show the duration of each task.
This way you have all the information you need to design a simple precedence diagram.
To start creating the precedence diagram, each activity is represented as a node.
Each box should have an arrow connecting it to the next step: the first activity will start on the left followed by the second, which will be connected by an arrow.
If the next two activities have the same predecessor, they will be stacked on top of each other with two arrows coming from the same starting point.
Conversely, when an activity has two predecessors, the arrows from those predecessors will both connect to the given activity.
In this way a basic precedence diagram is created.
What are the four dependencies in precedence diagrams?
To create a precedence diagram, you must master dependencies.
A dependency is an activity that depends on another task to be completed.
More specifically, there are four types of dependencies:
1. Mandatory dependency
A mandatory dependency is an obligatory dependency, such as adding water to the pool after it is built. You cannot add the water first and build the pool around it.
2. Discretionary dependency
A discretionary dependency helps in optimizing resources. Using the previous example: there is no strict logic for building the sides of the pool. Starting with one side is just as likely and important as another. However, there may be a reason to start with one rather than the other.
3. External dependency
An external dependency is beyond the project team’s control. Again, using the pool example, there could be bad weather that prevents digging from starting or a approval process that takes longer than expected.
4. Internal dependency
An internal dependency is a controllable dependency. If there is only one shovel, two people cannot dig the hole for making the pool. In this case, the program must include a way to split the work between the two people or purchase another shovel.
Each dependency, in turn, can be defined in four ways:
Finish to start : The activity cannot start until another one is finished. The most common dependency type used among activities.
Finish to finish: the activity cannot end until another one is finished.
Start to start: the activity cannot begin until another activity has begun.
Pros and cons of the precedence diagram method
This method offers a number of advantages to project management:
- Helps in finding relationships and dependencies between activities. This thus supports planning and risk prevention. If an activity is missing, it is easier to identify it.
- Helps pinpoint the critical path and critical activities and focus on them. Any delay in critical activities will delay the overall program.
- A precedence diagram is a great communication tool. Stakeholders can review activities at any time and get an understanding of the overall program.
- Helps to identify a potential bottleneck and implement appropriate changes.
- Provides a graphical representation of milestones, overall project duration, and the end of the project.
As for the cons:
- For large, complex projects, there will be thousands of tasks and dependency relationships. Without a project management software that features the appropriate functionality, it can be very difficult to manage them. To make matters worse, if the plan changes during the project lifecycle, the precedence diagram will need to be reviewed and redesigned, and again, without the appropriate software, this could become very cumbersome.
- One of the pros of having a project precedence diagram is that it allows the team to stay focused on the project activities and the stakeholders to keep an overview of the entire process. However, in case of large projects involving thousands of activities, it may be difficult to visualize the precedence diagram of the entire project without having to break it down into smaller parts.
The fine art of using precedence diagrams, therefore, is to find the appropriate level of detail.
The more tasks are presented, the greater the project overview will be, yet the more dependencies will be resulting and the more difficult it will be to manage the precedence diagram over time.
This is why the use of proper project management software becomes crucial.
This provides the foundation for determining the critical path of the project, predicting shortcomings, and understanding the possible reallocation of resources to solve problems.
Proper use of the precedence chart will provide the project manager with information about the status of the project and make it easier to control activities and schedules.