There are many types of relationships defined in project management. Relationships of tasks are very important because it allows project managers to determine the order of the tasks to be executed. One of the types of dependencies in a project life cycle is the mandatory dependency.
Mandatory dependency refers to a relationship that is inherent in the nature of work. This means that the tasks are contractually required therefore no other tasks should be implemented until the needs of the mandatory tasks are satisfied.
The nature of the work dictates the order for this particular project management dependency. For instance, before you can proceed to paint the walls, it is important that construction of the walls have been completed already.
So when is a mandatory dependency used? It is often utilized when project activities have physical or contractual limitations. The limitations make it difficult for the project manager to impose on the implementation of other activities unless the limitations have been fulfilled. This is the reason why this type of dependency is also termed as a hard dependency or hard logic.
This term is defined in the 5th edition of the PMBOK.