There are 4 types of dependencies in project management viz. Mandatory, Discretionary, External, & Internal. You will find definitions, detailed description, and examples of different types of schedule dependencies in this article.
Project Dependencies are, in fact, Schedule Dependencies. It simply means that schedule of one task or activity is reliant on another one. To understand the foundational concepts, you should read my previous article. It explains the project dependencies with the help of an example and differentiates between dependencies, assumptions, and constraints.
Some authors treat dependencies in project management and activity relationships anonymously but they are different from each other. I have written more about the similarities and differences between these terms later in the article.
Types Of Dependencies In Project Management
Mandatory Project Dependencies or simply mandatory dependencies are also called Hard Logic. These dependencies are legally or contractually required. They are, sometimes, inherent in the nature of the work.
As an example, 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 a Floor
- A – Build Car Prototype; B – Perform Crash Testing
Discretionary Project Dependencies or simply discretionary dependencies are defined by the Project Team. These are also called Preferred Logic, Preferential Logic or Soft Logic.
Sometimes, there is more than one way to define a sequence between 2 activities but the Project Team decides to take one sequence over the other. They choose a particular sequence because of the best practices or lessons learned from prior experiences.
As an example, 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 or simply external dependencies are defined between project activities and non-project activities.
The project activities are done by the Project Team. 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 within the same organization. The Project Team usually does not have control over non-project activities.
As an example, 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 or simply internal dependencies are defined between two project activities. The Project Team, usually, has complete control over the project activities.
As an example, 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
Project Dependencies vs Activity Relationships
You would have noticed that I have not talked about activity relationships in this article.
Activity relationships are closely related to project dependencies but they have a different meaning. In some project management literature you will find the terms dependency and relationship used interchangeably, which is factually incorrect.
A dependency just suggests that one activity is reliant on another activity but a dependency does not tell how an activity is reliant on another. e.g. in one situation activity A will start after activity B starts but in another situation activity A would start after activity B finishes. In both these situations activity A is dependent on activity B but the relationships are completely different.
All 4 dependencies can be expressed for all 4 relationships.
Final Words – Conjunction Of Project Dependencies
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? Can you share any examples from your project?
Please share your thoughts and leave a comment below.