Determining Activity Sequencing and Dependencies

Determining Activity Sequencing and Dependencies

Introduction to Activity Sequencing and Dependencies

Activity sequencing and determining dependencies is a crucial process in project schedule development that establishes the logical relationships between project activities. This process creates the framework upon which the entire project schedule is built.

Why Activity Sequencing and Dependencies are Important

Proper sequencing of activities is essential because it:

• Ensures activities are performed in a logical order
• Helps identify the critical path of the project
• Enables accurate schedule development and timeline estimation
• Facilitates resource allocation and optimization
• Provides a foundation for schedule compression when needed
• Allows for effective risk management and contingency planning

Understanding Activity Dependencies

Dependencies represent the relationships between activities that determine the sequence in which they must be performed. The four main types of dependencies in project management are:

1. Finish-to-Start (FS): The most common dependency where a successor activity cannot start until a predecessor activity finishes.
Example: Concrete must set (finish) before framing can begin (start).

2. Start-to-Start (SS): A successor activity cannot start until the predecessor activity starts.
Example: Once mixing concrete begins (start), pouring can begin (start) with some lag time.

3. Finish-to-Finish (FF): A successor activity cannot finish until the predecessor activity finishes.
Example: Final inspection (finish) cannot occur until all testing procedures are completed (finish).

4. Start-to-Finish (SF): A successor activity cannot finish until the predecessor activity starts.
Example: The night shift cannot end (finish) until the day shift begins (start).

Types of Dependencies

Mandatory Dependencies (Hard Logic): Physical limitations that cannot be changed.
Example: Paint must dry before applying a second coat.

Discretionary Dependencies (Soft Logic): Best practices or preferred sequences.
Example: Testing may be scheduled after development, though they could overlap.

External Dependencies: Relationships between project and non-project activities.
Example: Waiting for regulatory approval before proceeding.

Internal Dependencies: Relationships between project activities under the team's control.
Example: Design must be approved before coding begins.

Methods for Determining Activity Sequences

Precedence Diagramming Method (PDM): The most common approach that uses boxes (nodes) to represent activities and arrows to show relationships. PDM allows for all types of dependencies (FS, SS, FF, SF).

Arrow Diagramming Method (ADM): A traditional method where activities are represented as arrows and nodes represent the start and finish points. ADM only allows for finish-to-start relationships.

Conditional Diagramming Methods: Advanced techniques that incorporate conditional logic and decision points into the schedule network.

Process for Determining Activity Sequencing

1. Identify all project activities from the WBS and activity list
2. Analyze each activity to determine its relationship to other activities
3. Determine the type of dependency (FS, SS, FF, SF)
4. Identify the nature of dependencies (mandatory, discretionary, external, internal)
5. Document dependencies and their justification
6. Create a network diagram to visualize the sequence
7. Review and validate the sequence with subject matter experts
8. Update the sequence as needed throughout the project lifecycle

Tools for Activity Sequencing

• Network diagrams (PDM, ADM)
• Schedule management software (MS Project, Primavera)
• Dependency determination guidelines and templates
• Expert judgment and historical information
• Rolling wave planning for future project phases

Common Challenges in Activity Sequencing

• Incomplete understanding of technical requirements
• Over-sequencing, which limits scheduling flexibility
• Under-sequencing, which creates unrealistic schedules
• Failure to identify external dependencies
• Circular logic (loops in the network diagram)
• Dangling activities (no predecessor or successor)

Exam Tips: Answering Questions on Determining Activity Sequencing and Dependencies

Key Concepts to Master:

• The four types of dependencies (FS, SS, FF, SF) and when each is appropriate
• Differences between mandatory, discretionary, external, and internal dependencies
• Network diagramming methods and notations
• Lead and lag time applications
• Critical path identification based on dependencies
• Schedule compression techniques influenced by activity sequencing

Question Strategies:

• Read scenarios carefully to identify clues about required sequencing
• When presented with network diagrams, trace through the dependencies methodically
• For calculation questions, draw your own network diagram to visualize relationships
• Remember that Finish-to-Start is the most common dependency type
• Look for "gotcha" questions that mix up dependency types
• Pay attention to wording around constraints vs. dependencies

Practice Tips:

• Work through sample network diagrams to become familiar with all dependency types
• Practice determining critical paths based on different dependency scenarios
• Review case studies where poor sequencing led to project issues
• Create your own dependency scenarios and analyze their impact on scheduling
• Study the impacts of leads and lags on different dependency types

Sample Question Approach:

Question: "Activity B has a Start-to-Start relationship with Activity A with a 5-day lag. Activity A starts on day 10 of the project. When is the earliest that Activity B can start?"

Thinking process: Since this is a Start-to-Start (SS) relationship with a 5-day lag, Activity B can start 5 days after Activity A starts. Activity A starts on day 10, so Activity B can start on day 15.

This type of question tests your understanding of dependency types and lag time calculations, which are fundamental to activity sequencing knowledge.

Conclusion

Mastering activity sequencing and dependencies is essential for effective schedule management. By understanding the types of dependencies, their application, and how they impact the overall project timeline, project managers can develop realistic schedules and successfully guide projects to completion.