How To Create A Precedence Diagram

How to create a precedence diagram

A precedence diagram is created using methods from graph theory, like nodes (generally represented by rectangles) and arrows. A node consists of a presentation element describing a connection point and an arrow of a presentation element to describe the relationship between two nodes. One way is a sequence of arrows (also called edges).
As a connection point or a fact, precedence diagrams recognize processes, events and arrangement relationships:

Process: Activity with determined earliest and latest start and end points.

Event: Defined and recorded state in project schedule.

Relationships: Professional, personal and technical dependencies between individual processes; always consist of exactly two nodes.

This means: nodes can be represented as either processes or events. Arrows are processes or relationships. Exactly what they are depends on the selected precedence diagram method. The process node precedence diagram has been proven in practice and distributed in project management. This precedence diagram presents processes, that means a project's activities, through nodes, and connects them with arrows as an arrangement relationship.

Each precedence diagram always needs a start node – like the project start – an end node – its end. Then you can define, describe and place all further processes in a relationship. Only then does the actual "work" with the precedence diagram begin: the time calculations for each process node.

Which calculations does the process in the precedence diagram contain?

Precedence diagram legend

Each process node contains the name of the activity, a number, a total duration, and two points each for the start and the end of the activity and for the buffer. The entry of the figures corresponds to the rounded-off person-days. In this example you can see that the 2nd activity will take 10 days. The earliest start point is the 20th day of the project. Because the activity should last a total of 10 days, the earliest end date is day thirty of the project. So we calculate a total of 143 days. So the latest starting point is the 163rd day of the project. It takes 10 days, so the result is that the 173rd day of the project is the latest end point.

With the help of these values, the real advantages of network plans can be used – the buffer time plays a big part here. Buffer contains the time reserves that you use to move the activity to later. So you can keep the fixed date for the end of the project despite delays.

The total buffer time tells you, for example, how many days you can move an activity without moving the latest possible starting point of the following activity.

The free buffer informs you as to how many days an activity can be delayed without moving the earliest start point for the next activity. The free buffer is never higher than the total buffer.