Intro to Project Management: Project Schedule Management - Precedence Diagramming Method, PDM FS SS FF SF

What This Is

The Precedence Diagramming Method (PDM) is a project scheduling technique used to create a project schedule network diagram. It helps project managers visualize and manage dependencies between tasks, ensuring that tasks are completed in the correct order. In a real-world example, imagine building a bridge: the construction of the bridge's foundation must precede the installation of the bridge's superstructure. PDM helps ensure that these tasks are scheduled correctly, minimizing delays and ensuring the project's successful completion.

Key Terms & Formulas

• Precedence Diagramming Method (PDM): A project scheduling technique used to create a project schedule network diagram.
• Forward Pass (FP): The process of calculating the earliest start and finish dates for each task in the project schedule.
• Backward Pass (BP): The process of calculating the latest start and finish dates for each task in the project schedule.
• Critical Path (CP): The sequence of tasks that determines the minimum duration required to complete the project.
• Critical Path Method (CPM): A method used to identify the critical path in a project schedule.
• Free Slack (FS): The amount of time a task can be delayed without affecting the project's critical path.
• Total Slack (TS): The amount of time a task can be delayed without affecting the project's critical path, including any dependencies.
• Lag: A delay between two tasks, represented by a positive value.
• Lead: An acceleration between two tasks, represented by a negative value.
• ES = EF - D (Early Start = Early Finish - Duration): Calculates the early start date for a task.
• LF = LS + D (Late Finish = Late Start + Duration): Calculates the late finish date for a task.
• LF = ES - FS (Late Finish = Early Start - Free Slack): Calculates the late finish date for a task.

Step-by-Step / Process Flow

1. Create a Work Breakdown Structure (WBS): Break down the project into smaller, manageable tasks.
2. Identify Task Dependencies: Determine which tasks must be completed before others can begin.
3. Create a Precedence Diagram: Use the WBS and task dependencies to create a project schedule network diagram.
4. Perform a Forward Pass: Calculate the earliest start and finish dates for each task in the project schedule.
5. Perform a Backward Pass: Calculate the latest start and finish dates for each task in the project schedule.
6. Identify the Critical Path: Determine the sequence of tasks that determines the minimum duration required to complete the project.

Common Mistakes

• Mistake: Failing to account for task dependencies when creating a project schedule.
• Correction: Identify and document task dependencies to ensure that tasks are completed in the correct order.
• Mistake: Not performing a backward pass to calculate late start and finish dates.
• Correction: Perform a backward pass to ensure that tasks are completed on time and that the project schedule is realistic.
• Mistake: Confusing free slack and total slack.
• Correction: Understand the difference between free slack and total slack to accurately assess task flexibility.

Exam Tips

• Tip: Be prepared to explain the difference between forward and backward passes.
• Tip: Understand how to calculate free slack and total slack.
• Tip: Be able to identify the critical path in a project schedule.

Quick Practice Questions

1. If the CPI is 0.8, is the project under or over budget? Answer: Under budget. Explanation: A CPI of 0.8 indicates that the project is completing tasks at a rate of 80% of the planned budget.
2. What is the formula for calculating the early start date for a task? Answer: ES = EF - D. Explanation: The early start date is calculated by subtracting the task duration from the early finish date.
3. What is the difference between free slack and total slack? Answer: Free slack is the amount of time a task can be delayed without affecting the project's critical path, while total slack includes any dependencies. Explanation: Free slack is the amount of time a task can be delayed without affecting the project's critical path, while total slack includes any dependencies that may affect the task's completion.

Last-Minute Cram Sheet

• Precedence Diagramming Method (PDM): A project scheduling technique used to create a project schedule network diagram.
• Forward Pass (FP): The process of calculating the earliest start and finish dates for each task in the project schedule.
• Backward Pass (BP): The process of calculating the latest start and finish dates for each task in the project schedule.
• Critical Path (CP): The sequence of tasks that determines the minimum duration required to complete the project.
• Free Slack (FS): The amount of time a task can be delayed without affecting the project's critical path.
• Total Slack (TS): The amount of time a task can be delayed without affecting the project's critical path, including any dependencies.
• ES = EF - D (Early Start = Early Finish - Duration): Calculates the early start date for a task.
• LF = LS + D (Late Finish = Late Start + Duration): Calculates the late finish date for a task.
• LF = ES - FS (Late Finish = Early Start - Free Slack): Calculates the late finish date for a task.
• CPI = EV / AC (Cost Performance Index = Earned Value / Actual Cost): Measures the project's cost performance.
• 'Decomposition' breaks down work, not activities – it creates the WBS, not the activity list.