In this article, You will find definitions, detailed description, and examples of different types of task dependencies in project management. There are 4 types of project dependencies viz. Mandatory, Discretionary, External, & Internal.
Note: This article does not talk about activity relationships. Activity relationships are closely related to project dependencies. Like dependencies, there are 4 types of relationships – Finish to Start, Finish to Finish, Start to Start and Start to Finish. All 4 dependencies can be expressed for all 4 relationships. In some project management literature you will find the terms dependency and relationship used interchangeably, which is factually incorrect.
Project Dependencies are better characterized as Schedule Dependencies. To understand the foundational concepts you should also read dependencies in project schedule.
4 Types Of Dependencies In Project Management
Mandatory Project Dependencies are are legally or contractually required. They are, sometimes, inherent in the nature of the work. They are also called Hard Logic.
Consider 2 activities A and B. If B has a Mandatory Dependency on A then it means action on B cannot be performed until Action on A has been completed. Let us look at following examples to understand:
- A – Requirements Documentation; B – Client Approval
- A – Lay Building Foundation; B – Construct Floor
- A – Build Car Prototype; B – Perform Crash Testing
Discretionary Project Dependencies are defined by the Project Team. There could be more than one way to define a sequence between 2 activities. The Project Team may prefer one sequence over the other. The team would choose their preferred sequence because of best practices or lessons learned from prior experiences. These are also called Preferred Logic, Preferential Logic or Soft Logic.
Consider 2 activities A and B. A and B can be independently performed or one can be performed after the other. The Project Team can chose to make B dependent on A. Let us look at following examples to understand:
- A – Develop System Module X; B – Develop System Module Y
- A – Furnish Room R; B – Furnish Room S
- A – Book Airline Ticket; B – Buy Insurance
External Project Dependencies are defined between non-project Activities and project activities. The non-project activities are done by people who are external to the Project Team e.g. representatives from Client’s organization, Vendors’ organization or any other external groups. The project activities, on the other hand, are done by the Project Team. The Project Team usually does not have control over non-project activities.
Consider 2 activities A and B. If B has an External Dependency on A then it would signify that B is a project activity while A is a non-project activity. Following examples will be helpful in understanding:
- A – Client Go-Ahead; B – Initiate Project
- A – Delivery of Equipment; B – Start Development
- A – Approval of Building Plans; B – Start Construction
Internal Project Dependencies are defined between two project activities. The Project Team, usually, has complete control over project activities.
Consider 2 activities A and B. If B has an Internal Dependency on A then it would signify that both A and B are project activities. These are performed by the Project Team members. There is no involvement of any external party. Let us look at following examples to understand:
- A – Develop System; B – Test System
- A – Construct Wall; B – Paint Wall
- A – Assemble Machine; B – Pack Machine
There are a total of 4 Types of Project Dependencies. However, only 2 are applicable at the same time. Project Dependency between 2 activities could be any one of the following:
Over To You
How do you use dependencies in your projects? Do you document them in a separate log? Are they shared with different stakeholders? Please share your thoughts and leave a comment below.