Part 85: Dependency Determination and Integration
(Project Schedule Management: Sequence Activities)

  • When we plan the sequence of activities for our project, we want to figure out which activities depend on other activities
  • Dependency Determination is a process to determine and classify dependencies
  • There are four attributes, which can be combined (Mandatory or Discretionary, and External or Internal)
    • Mandatory Dependencies
      • Legally or contractually required, or inherent in the work
      • Can be a physical limitation
      • Also known as “hard logic”
      • For example, we can’t paint the wall until we install the drywall.  We can’t start construction until we obtain a building permit.
    • Discretionary Dependencies
      • Determined through knowledge of best practices
      • Used when multiple sequences of activities are possible, but a specific sequence is preferred
      • Following a best practice reduces the project’s overall risk
      • Discretionary Dependencies must be fully documented because they can limit our scheduling options
      • Also known as “preferred logic”, “preferential logic”, or “soft logic”
      • For example, we can install the heating, ventilation, and AC (HVAC) before or after installing the electrical wiring.  The systems don’t depend on each other.  But it’s recommended to install the HVAC first (HVAC takes up more space in the walls and ceiling, so it would be difficult to install the HVAC after the electrical work is complete).
    • External Dependencies
      • External dependencies are a relationship between a project activity and a non-project activity
      • Usually outside of the project’s team’s control
      • For example, obtaining a building permit is an external dependency.  We can’t start construction without it.  We have no control over how long the government will take to grant it.
    • Internal Dependencies
      • Internal dependencies are relationships between project activities
      • Usually within the project team’s control
      • For example, we can’t install the shingles until the roof trusses are in place.