As a project manager, it’s easy to get a bit confused at the beginning of a project. The main confusion typically centers around prioritizing the activities. It is important to set a logical relationship among the activities so that everyone understands the nature and sequence of the project. It is also essential for the core project team to quantify the dependencies among the activities so that they can work in an ideal efficient manner and accomplish the project goals. Consequently, there must be specific planning in determining the dependencies. Remember that there will be some mandatory dependencies that need to be considered during the planning stages.

That’s why we have network diagrams. We need to know how to prepare a network diagram and familiarize ourselves with the contents of a network diagram. Before we get to those points, however, you should first know the definition of a network diagram.

What Is a Network Diagram in Project Management?

A network diagram is a graphical representation of a project and is composed of a series of connected arrows and boxes to describe the inter-relationship between the activities involved in the project. Boxes or nodes represent the activity description, and arrows show the relationship among the activities.

There must be a start and finish to each activity, and all the other activities fall within these parameters. There are so many ways to draw a network diagram but the two most commonly used methods are the precedence diagramming method (PDM) and the arrow diagramming method (ADM). Today, most project managers use the precedence diagramming process to draw their network diagram.

    Types of Project Network Diagrams

    As you begin your diagram, you need to decide which activity is the successor and which one is the predecessor. Then, you need to create a dependencies chart. But before creating this network diagram, you need to create a logical relationship between the activities.

    As a project manager, you need to analyze these dependencies before creating a network diagram. GERT is a modification network diagram, which allows loops among the activities. However, it is very rarely used nowadays. Nevertheless, a project manager should know the reasoning behind drawing a Network Diagram through GERT.

    The two main forms of project network diagrams, as mentioned earlier, are the precedence diagram method and the arrow diagram method. Let’s take a closer look at them.

    Arrow Diagram Method (ADM)

    Also called the activity network diagram, the ADM uses arrows to symbolize the project’s associated activities. Unfortunately, ADMs aren’t used much these days, though it’s still a good idea to be familiar with them in case you happen to find one in use.

    The ADM has the following characteristics:

    • The arrow’s tail represents the activity’s start, while the head shows the finish
    • The arrow’s length is a measure of how long the activity will take.
    • Each arrow connects a pair of boxes called “nodes,” which represent the beginning or end of one activity in the overall sequence. The starting node is sometimes referred to as the “i-node,” and the ending node is often called the “j-node.”
    • The chart can only show a “finish to start” logical relationship (see below)

    Precedence Diagram Method (PDM)

    The Precedence Diagram Method enjoys heavy use in today’s project management circles and is considered to be a more efficient method for ADMs. Each node, or box, represents an activity, while the arrows symbolize the relationships between different activities. Therefore, the arrows symbolize the diagram’s four types of logical relationships:

    • Finish to Start (FS): This is the pervasive form of dependency among the activities. It means you need to wait until the predecessor’s activity finishes before starting a successor’s activity. You can’t start the successor’s activity before ending the predecessor’s activity unless your project employs a schedule compression technique. However, if you are doing so, the quality will decline. In most cases, you cannot begin the next process in any of the above circumstances.
    • Start to Start (SS):  Dependencies are also a very important part of network diagrams. A predecessor’s activity can start, and after some time, the successor’s activity could begin without waiting for the completion of the predecessor’s activity. You can say that there is a partial dependency among the activities.
    • Finish to Finish (FF): The predecessor’s activity must finish before the successor’s activity finishes. This diagram type is now rarely used in project management.
    • Start to Finish (SF): Also very rarely used these days. The previous activity will begin when the successor’s activity finishes.

    Project managers can make a note of lead or lag times alongside the arrows. So, for example, if a task is going to need two weeks’ time before the next activity can start, the project manager can write “2 weeks” over the arrow that connects the two activities (or nodes).

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    A Word About GERT

    For the sake of completeness, let’s take a quick look at GERT. The Graphical Evaluation and Review Technique is a network chart that’s been around for more than half a century. It’s a sophisticated diagram that’s fallen out of general use, but still has some life left in it.

    GERT describes each activity with an arrow and uses nodes to connect the activities and determine the relationship between them (e.g., type and conditions). Each task features a pair of parameters: duration and probability of appearance.

    GERT contains three logical operators, describing incoming activities to the node:

    • XOR Alternative: Only one path is possible
    •  OR Alternative: One or more paths can be done
    • AND: All paths must be performed. This is the most common operator, which means that every incoming activity must occur before the outcoming one can begin.

    GERT has two relations that concern outgoing node activities:

    • Deterministic. Every outcoming activity is assigned a probability value of 1, meaning that every activity will be performed.
    • Probabilistic. Every outgoing activity has a certain probability of appearing.

    GERTs include Loops, which account for unacceptable outcomes that require the activity to be repeated. Project managers can calculate the probability of repeating an activity.

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    Advantages of Network Diagram

    It is very important to develop the Network Diagram before proceeding with the project work. A project manager should involve several stakeholders, including the core team members while preparing the Network Diagram. Even when a new team member(s) joins your project in between, a project manager can refer him/her to the Network Diagram so they can gain a better understanding of the project and catch up to everyone else.

    Note that there could be some mandatory dependencies that cannot be converted into soft logic dependencies. In this case, you need to adjust the Network Diagram accordingly, reflecting these scenarios. Based on this Network Diagram, you will get the overall project duration after incorporating the number of resources and the number of working hours (or any similar metrics) against every activity. Accumulating these elements lets you understand the project’s overall schedule. So now, you can see how important this tool is for a project manager in accomplishing the project’s goal.

    In quick summary, here are the main advantages of network diagrams:

    • They track dependencies and possible bottlenecks
    • They establish clear project workflows
    • They provide stakeholders with a visual representation of the project’s progress

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    The bottom line is a project manager should prepare a good Network Diagram so that it shows the right path for project success. If your Network Diagram is accurate, half of your project problems could be easily solved. If you’re a project manager, you should try to explain the importance of Network Diagrams to your team members and why they’re an effective means of executing the project.

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