According to the PMBOK Guide, dependencies are used in the Sequence Activities process to define the logical relationship between tasks. Dependencies are categorized into four types: Mandatory, Discretionary, External, and Internal.
* Mandatory Dependencies: These are often referred to as " hard logic " or physical dependencies. They are inherent in the nature of the work being performed or are contractually required.
* Inherent Example: You cannot erect a building ' s frame until the foundation has been poured and cured.
* Contractual Example: A government contract may stipulate that a safety audit must be completed before any public testing can begin.
* Significance in Scheduling: During the development of the schedule, mandatory dependencies limit the project manager's ability to compress the schedule through fast-tracking, as the sequence is fixed by physical laws or legal requirements.
Analysis of Other Options:
* A. External: These involve a relationship between project activities and non-project activities (e.g., waiting for a government permit or a delivery from a vendor). While they can be mandatory, the specific definition of being " inherent in the nature of the work " refers to the Mandatory category.
* B. Lead: This is not a type of dependency but rather an acceleration of a successor activity. A lead allows an acceleration of the successor activity (e.g., starting to write a report two days before the research is finished).
* C. Discretionary: Also known as " preferred logic, " " soft logic, " or " preferential logic. " These are based on best practices or specific sequences desired by the team, even though other sequences are possible. They are the opposite of mandatory dependencies.