If you are a project manager you must know about project dependencies, and task dependencies in project management.

What are Project Dependencies?

We can define dependencies in the project plan as "relationships between tasks".1

We will not be going into the too much details of how to manage dependencies in this article, but we will go over the varieties of task dependencies in a project, and list them below:

  • Finish-Start – as task 1 concludes, task 2 can start.  This task dependency is relatively common. Example, the requirements documents concluded, now the development of this iteration of the product starts.
  • Start-Start – as task 1 starts, task 2 also starts.  This task dependency is less common.  Example, as the bake potatoes is baking, we start making the gravy.
  • Start-Finish – as task 1 starts, task 2 concludes.  Example, the introduction of a new Product Lifecycle Management (PLM) system must be in place before closing the old PLM system.
  • Finish-Finish – as task 1 finishes, task 2 finishes. This task dependency is less common but used to compress the schedule.  Example, as the product testing finish, the test report can also finish.

Our team members are important to identifying, estimating, and sequencing the tasks.  It is during this sequencing that we create a schedule. The way we sequence the task, the task dependencies, will have an impact the project duration and probability of project success.

Projects and Dependencies in Project Management

Projects are a series of actions and activities, some of which are connected as in the quality of the previous activity, for example writing requirements that will then be used to design and develop the product.  Perhaps a better example is, I must put on my socks before I put on my shoes – assuming I am going to wear my shoes with socks.

I was in a meeting once, and one of the managers said it was best not to recognize dependencies.  The problem with this is, it is not for you to recognize or not recognize dependencies. Dependencies are like gravity; dependencies are there whether you decide to acknowledge.  You cannot walk off the end of a pier expecting to not hit the water because you do not recognize gravity.  We can however, take prudent actions in our schedule development, specifically, the sequence of the tasks in our project schedule.

I once worked with a project manager that used the term critical path – willy-nilly. Critical path has a very specific definition. In fact, working with this person at a supplier, and hearing the way they talked, was the catalyst for the first book.  Words mean things, and specific words, technical words mean specific things.  

When it comes to task dependencies in project management or project dependencies, the tasks on the critical path, and those associated dependencies are the items especially of note for achieving the project schedule – or not. In fact, it can be beneficial for all team members to sit for training or certifications – this can be an expedient way of developing a common lexicon with your team.

Let’s explore project dependencies and probability of tasks. Every task we undertake, bound by cost, schedule, and ability to achieve the objective, have an associated probability.  Let’s say a specific task has a probability of success (ability to meet the items above) of 90%.

Let’s assume, not usually valid but it makes the math easier, that each task is independent. That is, the quality of the previous task has no impact on the depending task.  This is not usually true, but this will be the best-case scenario.  For a sting of depending tasks, the probability of the total string of tasks is the product of the probability of each of the tasks.

Summary

Dependencies should not to ignored but thought through.  You can choose to not recognize project dependencies, that will not change these interactions.  We are better served to think through how to construct the task sequence – understand the dependencies and take prudent actions in the control of the tasks.  

This requires identifying metrics to predict the task, and whether we are meeting the cost, schedule, and quality of that effort. These metrics will help us to see if our plan and actual work are congruent.  

Knowing this is important for the critical path, less so for other sequences of tasks for what are obvious reasons if you know the definition of critical path.  In general, effective monitoring and control actions are required to bring a project to successful fruition.  

1 PM Glossary