When you differentiate the sequence of actions in a project, you need to pay attention to reliances between these actions. Some actions might require predecessor or beneficiary actions to be completed or started before they can be started or completed themselves. The PDM is a scheduling technique used in the ‘sequence actions’ process of the PMI methodology. It helps in creating an assignment program network diagram, which is an output used as an intake for the ‘develop program’ process.
PDM involves identifying and visualizing the arrangement and reliances of actions in a project or a part of a project, such as a workstream or a work package. The method allows for the reflection of four types of reliances, also known as logical connections, which are explained in the next section. These reliances establish the connection between beneficiary actions and predecessor actions, represented as nodes in the diagram. PDM is more flexible than the enterprise-on-node or enterprise-on-arrow method, as it allows for overlaps of actions.
What Are the Types of Reliances in PDM?
The Precedence Diagramming Method (PDM) encompasses four types of logical connections:
- Finish-to-Start (FS) reliance: In this connection, the precursor enterprise must be finished before the beneficiary enterprise can begin;
- Finish-to-Finish (FF) reliance: With this connection, the precursor enterprise must be completed before the beneficiary enterprise can be completed;
- Start-to-Start (SS) reliance: This connection requires the prototype enterprise to have initiated before the beneficiary enterprise can start;
- Start-to-Finish (SF) reliance: In this logical connection, the prototype enterprise must have started before the beneficiary enterprise can be completed. It’s important to note that this type of reliance is not very common in procedure, as conceded.
To remember these concepts, focus on the first part of each connection’s name. For example, in “finish-to-start,” the prototype enterprise must accept the “finish” situation for the beneficiary enterprise to attain the “start” status.
Now, let’s move on to the next section, where we’ll provide definitions and examples of each of these types of reliances.
Remember, if actions have multiple logical connections, prioritize the more important one to avoid complexity and circular considerations in the diagram. Additionally, if actions can begin earlier or require to be hindered within a sequence, you can incorporate principles and lags. To learn more about principals and lags, refer to the relevant writing.
Example of Precedence Diagramming Method
Let’s take a fictional software enlargement project as an example of how the Precedence Diagramming Method (PDM) can be applied. Remember that you can adapt this example to various project types, such as construction, research and enlargement, or strategy enlargement and implementation.
To represent these reliances in a logical format, we use the four types of logical connections: Finish-to-Start (FS), Finish-to-Finish (FF), Start-to-Start (SS), and Start-to-Finish (SF). The following table illustrates these connections in the context of our example.
| Technical reliances | Logical connection |
|---|---|
| The completion of the technical design for module B is dependent on the completion of the technical design for module A. | enterprise (1) serves as the predecessor for enterprise (2) through a finish-to-finish (FF) reliance. It is important to note that while a start-to-start (SS) reliance may also exist between (1) and (2), the FF connection takes precedence due to its greater impact. |
| The completion of the technical designs for module A is a prerequisite for initiating the enlargement of module A. | enterprise (1) precedes enterprise (3) in a finish-to-start (FS) connection. |
| The completion of the technical designs for module B is necessary before commencing the enlargement of module B. | enterprise (2) comes before enterprise (4) in a finish-to-start (FS) connection. |
| The initiation of module B’s enlargement is contingent upon the commencement of module A’s enlargement. | enterprise (3) serves as the predecessor for enterprise (4) through a start-to-start (SS) connection. |
| The completion of feature F’s enlargement is not possible until the commencement of module B’s enlargement. | enterprise (5) follows enterprise (4) and is connected through a start-to-finish (SF) connection. |
Note that the reliances in this table deviate from those in the example in the leads and lags article for illustration purposes.
Determining Project Duration using Precedence Diagramming Method (PDM)
Once you have created the Precedence Diagram using the Precedence Diagramming Method (PDM), you can utilize it to calculate the total duration of the project or specific work packages, such as “technical design” and “enlargement.” Assuming no constraints other than logical connections exist (such as resource or material constraints), the sequence and schedule can be determined as follows:
- Design and enlargement of module A: This process takes a total of twenty five days (ten days for design + fifteen days for enlargement);
- Design and enlargement of module B: Initially, it would take twenty five days ( five days for design + twenty days for enlargement). However, the design of module B cannot be completed until the design of module A, which takes ten days, is finished. Therefore, the path for the design and enlargement of module B extends to thirty days (twenty days for enlargement + ten days for the design of module A). This duration accounts for the longer design duration of module A in comparison to the five-day Finish-to-Finish (FF) related design enterprise of module B. In our example, this longer path would also be considered the critical path, representing the chain of actions with the longest overall duration;
- Developing feature D: This enterprise takes 1 day and can be completed within the timeframe of the module B enlargement. As a result, it does not affect the overall project duration.
So the Precedence Diagramming Method (PDM) is a valuable and commonly used technique for identifying and visualizing the logical connections between actions. It is an important topic that may be covered in the Project Management Professional (PMP) exam.
The results obtained through PDM serve as input for developing the project schedule baseline. When sequencing and scheduling actions, one of the primary objectives is to identify the critical path, which is the longest sequence of actions determining the minimum project duration. The PDM provides essential data for the critical path method.
Importance of Logical connections in Project Management
Logical connections play a vital role in project management as they determine the sequence and reliances between actions. By understanding these connections, project managers can effectively plan and schedule actions, ensuring smooth project execution and successful delivery. Let’s explore why logical connections are important and how they contribute to project success.
- Ensuring Order and Coordination: Logical connections help establish a clear order of actions, ensuring that tasks are executed in the right sequence. For example, in a construction project, pouring concrete cannot begin before the foundation has been laid. By identifying and adhering to logical connections, project managers can avoid confusion and coordinate actions efficiently;
- Minimizing Rework and Delays: When actions are not properly sequenced, rework and delays become more likely. For instance, imagine if the enlargement of a software module began before its technical design was completed. This could lead to misunderstandings, changes, and ultimately, wasted time. By following logical connections, project teams can minimize rework, reduce delays, and maintain project momentum;
- Identifying Critical Paths: Critical paths are the longest sequence of actions that determine the minimum project duration. By understanding logical connections, project managers can identify the critical path and prioritize actions accordingly. This allows them to focus resources and efforts on actions that have the greatest impact on project timelines, ensuring timely project completion;
- Managing Constraints: Logical connections help project managers manage various constraints, such as resource availability, reliances, and constraints imposed by external factors. By considering these constraints and aligning actions based on logical connections, project managers can optimize resource allocation and mitigate potential bottlenecks;
- Enhancing Risk Management: Logical connections are closely tied to project risks. By analyzing reliances between actions, project managers can assess the impact of potential risks on the project schedule. They can identify actions that are more susceptible to risks and develop contingency plans to mitigate their effects. This proactive approach to risk management helps ensure project resilience and reduces the likelihood of schedule disruptions.
One of the major advantages of using the PDM in project management is its ability to highlight the critical path. The critical path is the longest sequence of dependent actions that determine the minimum project duration. By identifying the critical path, project managers can allocate resources and manage timelines more effectively.
The critical path provides valuable insights into which actions have the most significant impact on the project schedule. These actions must be carefully monitored and managed to ensure they stay on track, as any delay in the critical path activities will directly impact the project’s overall timeline. By focusing on the critical path, project managers can prioritize their efforts and allocate resources accordingly.
Furthermore, the critical path helps project managers identify potential bottlenecks and areas where risks may have a more significant impact. By proactively addressing these areas, project managers can mitigate risks, minimize delays, and increase the chances of successful project completion.
To wrap up
It’s important to note that the critical path may change throughout the project lifecycle as new dependencies or constraints arise. Regularly reviewing and updating the project schedule, considering any changes in dependencies or resource availability, ensures that the critical path remains accurate and up to date.
In conclusion, logical connections are fundamental to effective project management. They provide a roadmap for enterprise sequencing, coordination, and risk management. By leveraging logical connections, project managers can optimize project schedules, mitigate risks, and deliver successful outcomes. It is crucial for project teams to understand and incorporate these connections into their planning processes to achieve project objectives efficiently.