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Project dependencies flowcharts

What are dependencies in project management?

Every project has dependencies, which Max Wideman’s Glossary defines as the “relationships between products or tasks”, i.e. tasks that require input from other tasks to be completed, or activities that can’t start until a previous activity is done. There are often several sequences to a task, and they’re all dependent on each other. The scope of a project requires these tasks to be completed in order.

Why do we need project dependencies?

Setting out the project’s dependencies is crucial to its overall success. A project manager needs to:

  • Lay out the sequences of tasks within the project plan.
  • Calculate the tasks’ critical paths, i.e. how long each one is going to take.
  • Identify the necessary resources to complete the tasks, as well as potential scheduling issues.
  • Monitor and manage tasks as part of the overall project plan.
  • Identify and action any opportunities to accelerate the project’s task schedule.

Examples of dependencies in project management

Let’s say you’re doing a construction project and have to build, plaster and paint a wall. The plastering can’t start until the wall has been built, and the necessary pipes and wiring have been fitted. The wall can’t be decorated until the plastering has been done, including around the pipes and wiring.

Some dependencies are external, rather than internal. In the previous example, the construction company building a wall may rely on third-party suppliers for building materials. Before they can even start building, they’ll also need licenses and planning permission.

Project dependency types

There are four types of dependencies in project management which define the relationships between tasks:

  1. Finish-to-Start – the first task needs to be completed before the second task can start, as per the example above.

  1. Finish-to-Finish – the second task can’t be completed until the first task has been done. For example, wires can’t be fitted into the wall until they’ve been inspected.

  1. Start-to-Start – the following task can’t commence until the first task has started. For example, a concrete floor can’t start to be levelled until the concrete has started pouring into the designated space.

  1. Start-to-Finish – the first task has to start before the second task can be completed. For example, a new software installation has to start before the old installation can be stopped.

Project dependency categories

As well as the types of dependencies, there are also dependency categories. These are logical, preference and resource-based:

  1. Logical dependencies, which are fundamental requirements.

  1. Preference dependencies, which have several schedule options but are based on the preferred path.

  1. Resource-based dependencies, which could be completed more quickly if additional resources were available.

Hard Logic vs Discretionary dependencies

Some project dependencies are mandatory, also known as Hard Logic dependencies, i.e. they‘re contractually or legally required as part of the project plan. Discretionary dependencies show there’s more than one path in a task or activity’s sequence. In that case, the team chooses their preferred order, usually based on experience.

How to manage project dependencies

Dependencies are often shown as Gantt charts, which can help:

  • Track the time a project is taking to complete
  • Decide and allocate resources
  • Order the tasks
  • Aid the management of dependencies between tasks.

Other tools include a Logic Network that shows the sequence of tasks or activities that logically come before or after a different activity or task. A PERT chart – the Program Evaluation and Review Technique – is useful for analysing tasks involved in a project. It lays out the minimum time needed to complete the project, showing a hierarchical breakdown of the project requirements.

Other diagrams that are particularly useful within the project plan for easy referencing by team members are:

  • Cause and Effect diagrams
  • Flow and control charts
  • Histograms
  • Scatter diagrams
  • Pareto Charts and Pareto Analysis.

Managing dependencies within a project will help both the project manager and team work and manage tasks in their best possible order. This helps ensure a project is completed on time, if not ahead of time.