Explain each and provide refernces:

• A network diagram provides a visual representation of a project's schedule. It describes the actions that must be followed in the proper sequence to complete the project on time. The critical route, a set of tasks, determines the project's minimum completion time. The project must be delayed in order to complete tasks that are on the critical path.
• The critical path is the longest path in the network diagram. The project's minimal completion time depends on the sequence in which the tasks are finished. The project must be delayed in order to complete tasks that are on the critical path.
• The critical path method (CPM) is a technique for organizing, scheduling, and managing projects. It is commonly used in manufacturing. Morgan R. Walker and James E. Kelley Jr., two DuPont employees, invented the critical route technique for the first time in 1957.