4 Types of Dependencies In Project Management – Definitions & Examples

schedule dependencies in project management

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

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

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

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

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

Concluding Remarks

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:

  • Mandatory-External
  • Discretionary-External
  • Mandatory-Internal
  • Discretionary-Internal

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.

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Praveen Malik, PMP

​Praveen Malik ​is a certified Project Management Professional (PMP®) with a rich 23+ years of experience. He is a leading Project Management Instructor, Coach and ​Advisor. He ​has successfully trained thousands of aspirants for the PM certification exams.

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Viridiana Reply

Thank you. Was looking for some examples.

    Engdaw Reply

    Thanks. I am from Ethiopia, my name is Engdaw Admasu.
    I did read this posts and get some best understandings.

    Mona Yunan Reply

    hi, I was also looking for good examples. thanks.

    Abdul Reply

    Many thanks for the clarification!!

    Abdulrahamn

Vine Cardenas Reply

thank you for the information

Michael Etoedia Reply

Thanks for the clarity, I just stumbled on the different types of dependencies and wanted to know more about it then your site provided a very good explanation with examples to it, thanks and keep up the good work

One more thing though, looking at the dependencies, it kind of sounds like the internal dependencies can also be mandatory dependencies, or what is your take on that.

    Praveen Malik, PMP Reply

    Thanks Michael. Please look at the “Concluding Remarks” in the article. I have mentioned there 4 different combinations: Mandatory-Internal is one of them.

Sathudri Reply

Thanks a lot..it was helpful..

    Praveen Malik, PMP Reply

    Thanks Sathudri

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