The convention used in network diagramming of relationships and leads and lags is that the relationship is shown on the logical arrow only if it is not a finish-start relationship. If there are no leads or lags, no designation is given.
Project Start and Project Finish Events
Each activity in the diagram will always have a predecessor and a successor if the following convention is used. The convention is to create two events, the start of the project and the finish of the project. An event is a project activity that has zero duration and marks a place of significance in the project. Creating a start and finish event for the project allows all other activities to have at least one predecessor and at least one successor. ...