A Dependency is a logical relationship between two or more activities, where the timing, sequencing, or completion of one activity depends on another. Dependencies define the order of execution in a project schedule and impact overall project flow.

Key Aspects of Dependencies

  • Control Task Sequencing – Dictate the order in which tasks must be performed.
  • Impact Schedule Management – Delays in dependent tasks can affect project deadlines.
  • Can Be Mandatory or Discretionary – Some dependencies are fixed, while others are based on best practices.
  • Essential for Critical Path Analysis – Help determine the longest project duration.

Types of Dependencies

TypeDescriptionExample
Finish-to-Start (FS)Task B cannot start until Task A is finished.A house cannot be painted until construction is completed.
Start-to-Start (SS)Task B can start only after Task A has started.Coding and testing can begin simultaneously after requirements are finalized.
Finish-to-Finish (FF)Task B cannot finish until Task A is finished.Final editing of a book cannot be completed until writing is finished.
Start-to-Finish (SF)Task B cannot finish until Task A has started.A security shift cannot end until the next shift has started.

Mermaid Diagram: Dependency Example

graph LR;
    A["Task A: Lay Foundation"] -->|FS| B["Task B: Build Walls"]
    B -->|FS| C["Task C: Install Roof"]
    C -->|FS| D["Task D: Paint Exterior"]
    B -->|SS| E["Task E: Start Interior Work"]
    D -->|FF| F["Task F: Final Inspection"]

Example Scenarios

Software Development

A code review (Task B) cannot begin until code implementation (Task A) is completed (Finish-to-Start dependency).

Construction Project

Plumbing installation (Task B) must start at the same time as electrical wiring (Task A) (Start-to-Start dependency).

Event Planning

A marketing campaign launch (Task B) cannot be completed until advertising content creation (Task A) is finalized (Finish-to-Finish dependency).

Why Dependencies Matter

  • Ensure Logical Task Sequencing – Define relationships between project activities.
  • Improve Scheduling Accuracy – Helps in setting realistic deadlines.
  • Identify Bottlenecks Early – Allows proactive risk mitigation.
  • Support Critical Path Analysis – Helps determine key project constraints.

See also: Critical Path Method (CPM), Task Sequencing, Project Schedule, Lead and Lag Time.