What is a project network diagram?

A graphic or tabular schedule

The project network diagram displays the duration of activities in the project, their chronological order and logical dependencies between the activities graphically or in tabular form.
Unlike the work breakdown structure (WBS), a network diagram also takes into account the chronological order of activities according to their dependencies, and not just the logical order of the project activities. Bar charts such as Gantt Charts are a special form of the network diagram.

Main functions of a network diagram are:

Determination of the total duration of the project
Representation of the logical and chronological order in the project
Risks: Where is the critical path? Where are potential bottlenecks in the project process?
Opportunities: Where can the project process be streamlined?

The network diagram is the foundation for the project scheduling.

In modern project management, hardly any network plans are calculated “manually” anymore. Project managers use a project management software to do so. However, understanding the basics of the method enable you to better understand your own project plan.

Basic elements of the network are activity nodes. For example: In the project “Employee Survey”, one activity node can be “Creation of the questionnaire”. An activity node includes the following information:

Duration (d)
Activity number
Earliest start time (EST)
Latest start time (LST)
Earliest finish time (EFT)
Latest Finish time (LFT)
Total or cummulative buffer (CBT) (= LST – EST or = LFT – EFT)
Free buffer (BT) (= EST of the successor – EFT of the current activity)

The earliest finish time (EFT) is derived from the earliest start time (EST) and the activity’s duration (d). The latest finish time minus the activity duration (d) results in the latest start time (LST).

Here is a step-by-step guide on how to conduct an example network analysis: Back to Basics (Part 10): How to Create a Project Network Diagram