Precedence Diagram Method Arrow

The Arrow: A Powerful Symbol in Project Planning with the Precedence Diagram Method (PDM)

The Precedence Diagram Method (PDM) is a powerful tool for project planning and scheduling, offering a clear visual representation of project activities and their dependencies. Central to PDM is the use of arrows, which serve a critical purpose beyond simply connecting activities. These arrows represent lags, the relationships and constraints between tasks, providing crucial information for effective project management.

What are Lags?

Lags in project management describe the temporal relationship between activities. They define how long one activity must be delayed before another can start. There are several types of lags:

Finish-to-Start (FS): The most common lag, where one activity must finish before the next can start.
Start-to-Start (SS): Requires a specific delay between the start of two activities.
Finish-to-Finish (FF): One activity must finish before the other can finish.
Start-to-Finish (SF): One activity must start before the other can finish.

The Power of the Arrow

In PDM networks, arrows are used to visually depict these lag relationships:

Arrow Direction: The direction of the arrow indicates the type of lag. For example, a Finish-to-Start lag is shown with an arrow pointing from the tail of the first activity to the head of the second activity.
Arrow Length: The length of the arrow has no significance; it simply connects the activities.
Lag Value: The lag value, representing the specific delay, is written above or below the arrow.

Benefits of Using Arrows in PDM

Clarity and Visual Communication: Arrows provide a clear and intuitive representation of activity dependencies, making it easy to understand the flow of the project.
Precise Scheduling: The lag values associated with arrows allow for precise scheduling, ensuring activities start and finish at the appropriate times.
Identification of Critical Path: Arrows help to identify the critical path, the sequence of activities that directly impact the project's overall duration.
Resource Allocation Optimization: Understanding the relationships between activities through arrows helps optimize resource allocation and ensure efficient use of personnel and materials.

Example: Building a House

Imagine building a house. The activity "Lay Foundation" must finish before the activity "Build Walls" can begin. This Finish-to-Start lag is represented by an arrow pointing from the "Lay Foundation" activity to the "Build Walls" activity.

Conclusion

The arrow is a powerful and versatile symbol in the Precedence Diagram Method (PDM) for project planning and scheduling. By representing lags and dependencies between activities, these arrows provide essential information for project managers, enabling efficient planning, scheduling, resource allocation, and ultimately, successful project completion.

Test Your Knowledge

Quiz: The Arrow in Precedence Diagram Method (PDM)

Instructions: Choose the best answer for each question.

1. What does an arrow in a PDM network primarily represent? (a) The duration of an activity (b) The cost of an activity (c) The relationship between activities (d) The resources needed for an activity

Answer

2. Which type of lag requires one activity to finish before the next can start? (a) Start-to-Start (SS) (b) Finish-to-Finish (FF) (c) Start-to-Finish (SF) (d) Finish-to-Start (FS)

Answer

(d) Finish-to-Start (FS)

3. What is the significance of the length of an arrow in a PDM network? (a) It represents the duration of the lag. (b) It indicates the priority of the activity. (c) It has no specific meaning. (d) It shows the cost of the activity.

Answer

4. Which of the following is NOT a benefit of using arrows in PDM? (a) Clearer communication of project dependencies (b) More precise project scheduling (c) Easier identification of critical path (d) Improved project team motivation

Answer

(d) Improved project team motivation

5. In a PDM network, how is a Finish-to-Start (FS) lag visually represented? (a) An arrow pointing from the head of the first activity to the tail of the second activity (b) An arrow pointing from the tail of the first activity to the head of the second activity (c) An arrow pointing from the head of the first activity to the head of the second activity (d) An arrow pointing from the tail of the first activity to the tail of the second activity

Answer

(b) An arrow pointing from the tail of the first activity to the head of the second activity

Exercise: Planning a Birthday Party

Scenario: You're planning a birthday party for a friend. Use the Precedence Diagram Method (PDM) to visualize the activities and their dependencies.

Activities:

A: Choose a date and time
B: Send out invitations
C: Buy decorations
D: Prepare food and drinks
E: Set up the venue
F: Clean up

Dependencies:

A must be completed before B, C, D, E, and F.
C must be completed before E.
D must be completed before E.
E must be completed before F.

Instructions:

Draw a PDM network using arrows to represent the activities and their dependencies.
Indicate the type of lag (FS, SS, FF, SF) for each arrow.
Label the arrows with appropriate lag values if applicable (for example, 2 days between sending invitations and buying decorations).

Exercice Correction

Here's a possible PDM network for the birthday party planning:

PDM network for birthday party planning

**Note:** The lag values are not provided in the scenario, so you can use your own judgment to estimate them. For example, you might assume a 1-day lag between sending invitations and buying decorations.

Books

Project Management: A Systems Approach to Planning, Scheduling, and Controlling by Harold Kerzner: This comprehensive text covers various project management methodologies, including PDM, and provides detailed explanations of network diagrams.
Project Management: The Managerial Process by Gareth Morgan: A well-regarded book that explores project management principles, including scheduling techniques like PDM.
A Guide to the Project Management Body of Knowledge (PMBOK Guide) by the Project Management Institute: The industry standard guide for project management, it provides a thorough overview of PDM and other scheduling techniques.

Articles

"Precedence Diagramming Method (PDM)" by ProjectManagement.com: This article offers a clear explanation of PDM, its benefits, and how to create PDM networks.
"The Arrow Diagram Method" by the University of Central Florida: A concise explanation of the arrow diagram method, also known as the Activity-on-Arrow (AOA) method, which is closely related to PDM.
"Understanding Project Dependencies and Lags" by Planview: This article delves into the different types of dependencies and lags that influence project scheduling, emphasizing their importance in PDM.

Online Resources

Project Management Institute (PMI): https://www.pmi.org/ The PMI website provides a vast amount of information on project management, including resources dedicated to PDM and scheduling.
ProjectManagement.com: https://www.projectmanagement.com/ A valuable online resource offering articles, tutorials, and tools related to project management, including PDM.
MindTools.com: https://www.mindtools.com/commsskills/network-diagramming.htm This website provides a practical guide to network diagramming, explaining the concepts behind PDM and other methods.

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