A Project Network Diagram is a logical or technical representation of all the activities in a project showing their dependency relationships.
Those logical relationships are also known as:
In building the project activity network we are in a sense building a paper model of the method or process by which we intend to execute and deliver the project. There are different techniques for creating project activity networks. One method used is known as the precedence diagramming method or (PDM). This method uses a box (square, rectangle or any other shape you prefer) represents each activity with arrows (not lines) connecting these activities and representing the precedence (predecessor and successor) relationships.