Dependencies are defined as relationships among tasks that determine the sequence in which project management activities need to be performed.  These tasks may be multiple preceding tasks which mean that two tasks can be applicable at the same time.  They are also characterized by different attributes like being discrete, mandatory, external and internal which are also considered as the four types of dependencies.

Dependency is a technique used in identifying the appropriate type of dependency used to create the relationship between two activities. The activities are termed as predecessor (which refers to the first activity) and successor (the activity that precedes the first).

The mandatory dependency refers to  tasks that are stipulated in the contract thus they are inherent in the project. Failure to deliver the task involves a certain level of penalty. The discretionary dependency also referred to as preferred logic,  is established based on the knowledge of best practices. They are arbitrary thus, they should be documented for proper scheduling especially when updating or reviewing the project management plan.

External dependencies involve the relationship of project activities and those that are not related to the project. They are usually beyond the control of the project team. Examples of external dependencies include government environment hearings before construction project can begin and software testing.

The internal dependencies involve the relationship of different project activities that are within the control of the project team. This includes internal testing of product components before assembling the entire product.

The process of dependency determination requires the project manager or the project management team to determine them so that they can assign tasks to the team members and also inform the stakeholders. Moreover, it is easier to arrange the task if the dependencies are all identified.