Precedence Diagram Method Arrow

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

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)

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.

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

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

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:

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

Techniques

Chapter 1: Techniques of the Precedence Diagram Method (PDM) using Arrows

The Precedence Diagram Method (PDM) employs arrows to represent the relationships between activities within a project schedule. These relationships, or lags, are crucial for accurate scheduling and resource allocation. Several techniques are used in conjunction with arrows to define these relationships:

1. Defining Lag Types: As previously discussed, four primary lag types are represented using arrows:

• Finish-to-Start (FS): The most common. An activity cannot begin until the preceding activity is complete. The arrow points from the predecessor's finish node to the successor's start node.

• Start-to-Start (SS): A minimum time delay exists between the start of two activities. The arrow connects the predecessor's start node to the successor's start node. A positive lag value indicates the delay.

• Finish-to-Finish (FF): An activity cannot finish until a preceding activity has finished. The arrow points from the predecessor's finish node to the successor's finish node.

• Start-to-Finish (SF): Relatively rare. A preceding activity must start before a succeeding activity can finish. The arrow points from the predecessor's start node to the successor's finish node.

2. Representing Lag Values: The numerical value of the lag (delay in time units) is typically written above or below the arrow. A lag of zero indicates no delay. Negative lags are sometimes used to represent a constraint where an activity must start before the preceding activity completes (though this is generally avoided for clarity).

3. Node Representation: PDM diagrams use nodes (often circles or boxes) to represent activities. The arrows connect these nodes, clearly indicating the direction and type of dependency. The activity's name and duration are usually included within the node itself.

4. Network Construction: Creating the network diagram involves systematically identifying activities, determining dependencies, assigning lag types, and inputting lag values. This process requires a thorough understanding of the project's workflow and interdependencies.

5. Critical Path Analysis: Once the network is complete, critical path analysis can be performed. This involves identifying the longest path through the network, which represents the minimum project duration. Activities on the critical path have zero float (no flexibility in scheduling) and any delay on these activities will delay the entire project. Arrows are instrumental in visualizing this critical path.

Chapter 2: Models within the PDM Arrow Approach

Several models utilize the arrow-based representation of PDM:

1. The Basic PDM Model: This model simply represents activities as nodes and their dependencies as arrows with lag types and values. It's the foundation for more complex models.

2. Resource-Constrained PDM: This model extends the basic model by considering resource limitations. Arrows help visualize the dependencies and the impact of resource constraints on scheduling. Resource leveling or smoothing techniques can be applied, potentially adjusting lag values to optimize resource utilization while maintaining the project schedule.

3. Time-Cost Trade-off Models: These models explore the relationship between project duration and cost. Adjusting lags (and potentially activity durations) allows for evaluating different scheduling options with varying cost implications. The arrows visually display the impact of these changes.

4. Risk-Based PDM: This model incorporates uncertainty and risk into the scheduling process. Arrows can highlight activities with high uncertainty, allowing for contingency planning and risk mitigation strategies. The impact of potential delays on the critical path can be visually assessed.

5. Hybrid Models: In practice, PDM is often used in conjunction with other project management techniques. For example, combining PDM with Earned Value Management (EVM) allows for tracking progress and cost performance against the schedule visualized using the arrow diagram.

Chapter 3: Software for PDM Arrow Diagrams

Numerous software packages facilitate the creation and management of PDM networks using arrows. These tools offer features beyond basic diagramming:

1. Microsoft Project: A widely used project management software that supports PDM scheduling. It allows for defining activities, setting dependencies (lags), and visualizing the network diagram. Critical path analysis, resource leveling, and various reporting features are included.

2. Primavera P6: A more advanced project management software often used for large-scale projects. It offers similar features to Microsoft Project but with enhanced capabilities for complex scheduling, resource management, and risk analysis. Visual representation via arrow-based PDM diagrams is central to its functionality.

3. Asta Powerproject: Another robust project management software offering comprehensive PDM functionality, including various lag types, resource allocation, and advanced scheduling algorithms.

4. Open-Source Options: Several open-source project management tools offer basic PDM capabilities, although they might lack the advanced features found in commercial software.

5. Specialized Add-ins: Some software packages offer add-ins or extensions specifically designed for enhancing PDM visualization and analysis.

Chapter 4: Best Practices for Using Arrows in PDM

Effective use of arrows in PDM requires adherence to certain best practices:

1. Clear Activity Definition: Activities should be clearly defined and concisely described. Ambiguous activity descriptions can lead to incorrect dependencies and flawed scheduling.

2. Accurate Lag Definition: Ensure that lag types and values are precisely defined and reflect the actual relationships between activities. Inaccurate lags can significantly impact the accuracy of the schedule.

3. Consistent Notation: Maintain consistency in the notation used for arrows, lags, and activity representation throughout the diagram. This ensures clarity and avoids confusion.

4. Regular Review and Updates: The PDM network should be regularly reviewed and updated to reflect changes in the project scope, schedule, or resources.

5. Collaboration and Communication: The PDM diagram should be used as a collaborative tool, facilitating communication among project stakeholders.

6. Simplicity and Clarity: While comprehensive, the diagram should remain simple and easy to understand. Avoid unnecessary complexity. Use clear and concise labeling.

7. Verification and Validation: Before relying on the schedule, verify the accuracy of the network and validate the schedule through simulations or expert reviews.

Chapter 5: Case Studies of PDM Arrow Applications

Case Study 1: Construction Project: A large-scale building construction project employed PDM to manage the complex interdependencies between various activities like foundation laying, framing, electrical work, plumbing, and finishing. The arrow-based diagram facilitated precise scheduling, resource allocation, and risk management, leading to successful project completion within budget and timeline.

Case Study 2: Software Development: A software development project used PDM to track the dependencies between different coding modules, testing phases, and deployment stages. The arrow-based representation helped in identifying critical path activities, managing dependencies between developers, and optimizing resource allocation.

Case Study 3: Event Planning: A large-scale event like a conference or festival can benefit from PDM to schedule various tasks like venue booking, speaker coordination, marketing, logistics, and on-site management. Arrows help manage the intricate dependencies between these activities.

Case Study 4: Manufacturing Process: Manufacturing processes often involve complex sequences of operations. PDM can be used to model the workflow, highlighting dependencies and enabling optimization of production schedules.

Case Study 5: Research Project: In research, PDM can help sequence experiments, data analysis, and report writing, ensuring efficient use of resources and timely completion.

These case studies demonstrate the versatility of PDM and the power of its arrow-based representation across diverse project domains. The ability to clearly visualize dependencies and manage complex workflows makes PDM a valuable tool for project managers.