Precedence Diagramming Method (PDM)
The Precedence Diagramming Method (PDM) is a fundamental tool used in project scheduling for visually depicting the relationships between activities. In PDM, activities are represented as nodes (commonly rectangles), and dependencies between them are shown as arrows connecting these nodes. This method allows project managers to identify the sequence in which activities must be performed, establish the logical relationships, and determine the critical path of the project. There are four types of dependencies utilized in PDM to define the relationships between activities: 1. **Finish-to-Start (FS):** The successor activity cannot start until the predecessor activity finishes. This is the most common type of dependency. 2. **Finish-to-Finish (FF):** The successor activity cannot finish until the predecessor activity finishes. 3. **Start-to-Start (SS):** The successor activity cannot start until the predecessor activity starts. 4. **Start-to-Finish (SF):** The successor activity cannot finish until the predecessor activity starts. This type is rarely used. By employing PDM, project managers can effectively plan and control the project schedule. It facilitates the identification of potential scheduling issues early in the planning process, such as bottlenecks or resource conflicts. Additionally, PDM supports the application of critical path method (CPM) analysis to determine the minimum project duration and identify activities that have flexibility in their scheduling (float). Understanding and utilizing PDM is essential for efficient project scheduling and for communicating the project plan to stakeholders.
Precedence Diagramming Method (PDM) Guide
What is Precedence Diagramming Method (PDM)?
The Precedence Diagramming Method (PDM) is a project scheduling technique used to build a project schedule network diagram that graphically displays the project activities and their relationships. PDM is the primary method used in Critical Path Method (CPM) scheduling and is essential for understanding activity sequencing in project management.
Why is PDM Important?
PDM is crucial because it:
• Provides a visual representation of project workflow
• Helps identify dependencies between activities
• Enables calculation of the critical path
• Facilitates schedule optimization
• Helps in identifying potential scheduling conflicts
• Allows for effective resource allocation
• Supports proactive risk management
How PDM Works
PDM uses nodes (boxes) to represent activities and arrows to show relationships between them. The four types of logical relationships in PDM are:
1. Finish-to-Start (FS): The most common relationship where a successor activity cannot start until its predecessor activity finishes.
2. Start-to-Start (SS): A successor activity cannot start until its predecessor activity starts.
3. Finish-to-Finish (FF): A successor activity cannot finish until its predecessor activity finishes.
4. Start-to-Finish (SF): A successor activity cannot finish until its predecessor activity starts (rarely used).
Each relationship can include lead time (acceleration) or lag time (delay).
Creating a PDM Network Diagram:
1. Identify all project activities
2. Determine dependencies between activities
3. Draw nodes for each activity
4. Connect nodes with arrows showing relationships
5. Add duration estimates to each activity
6. Calculate early start, early finish, late start, and late finish dates
7. Identify the critical path and float
Exam Tips: Answering Questions on PDM
1. Know the terminology: Be familiar with terms like predecessor, successor, dependency types, critical path, float, and network diagram.
2. Understand relationship types: Memorize all four dependency types (FS, SS, FF, SF) and be able to identify them in diagrams.
3. Practice calculations: Be prepared to calculate early/late start/finish dates and identify the critical path.
4. Recognize diagram conventions: Learn how PDM diagrams represent activities, relationships, and critical paths.
5. Apply lag and lead time: Understand how lag (+) and lead (-) affect the schedule and can be noted on relationship lines.
6. Analyze scenarios: Practice analyzing how changes to activity durations or relationships impact the overall schedule.
7. Connect to other knowledge areas: Understand how PDM relates to risk management, resource allocation, and change management.
8. Watch for tricky questions: Exams may include questions asking you to identify errors in diagrams or determine impacts of changes.
9. Remember limitations: Be aware of PDM limitations such as not showing resource constraints by default.
10. Practice drawing: Be prepared to create small PDM diagrams based on given information.
Common exam mistakes to avoid include confusing the relationship types, overlooking lead/lag times, and calculating the critical path incorrectly. Focus on understanding both the theory and practical application of PDM.
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