So, what's the fuss about network diagrams anyway?
Schedules. Everywhere we go, we see one. Whether you're managing a travel itinerary or managing a major commercial project's development team, chances are you've got plenty of experience in thinking up simple ones, at least. But big projects are a lot more complicated than jotting down a note on the back of your hand with a sharpie.
Big projects need big tools.
Chances are, you don't need me to tell you that graphs and charts can be a lifesaver in management. The ability to see critical information in a clear, clean, visual manner in but a moment's glance is priceless. So, it should come as no surprise that big brains in project management have figured out a way to make the complex problem of schedule management a little easier.
Enter network diagrams.
Figure 1. (n.d.-b). Project-Managemant.info. https://project-management.info/project-schedule-network-diagram/
What is a network diagram?
A project schedule network diagram, or network diagram for short, is a visual map of the relationships between tasks within a project. At a glance, it provides a project manager a clear representation of important characteristics of tasks, their durations, and interdependencies, allowing a project manager to quickly break down the project into smaller tasks and see just what needs to be accomplished to get to whatever point in the project.[1]
How to interpret a network diagram
How to read a network diagram can be a little tricky at first, because it's mostly dependent on what kind of network diagram you're looking at. Yup, there's more than one kind. The good news for you is, that not only are they not too hard to figure out, but I'm also here to help you out.
In the simplest terms, network diagrams are visual representations of tasks, linked together in the order that they must be completed. A task may have two other tasks leading to it, meaning that it cannot be completed or even started until the other two have been.
Elements of a network diagram
Network diagrams may seem overwhelming at first, but they're actually very simple, just combinations of common elements.
Arrows
Nodes
Task names or IDs
Task Durations
Other important task information
Different types of network diagrams may use these elements differently, or not include some at all.
Activity on Arrow - AOA Diagram
Figure 2. (n.d.-b). Project-Management.info. https://project-management.info/wp-content/uploads/2020/04/Activity-on-Arrow-Diagram-AOA.webp
In AOA diagrams, also known as ADM (Arrow Diagram Method) diagrams, there are two main elements: Nodes, and arrows. Arrows represent tasks and may include other important information like estimated durations. The nodes, however, represent milestones: Concrete accomplished stages of the project development process. [2]
Activity on Node - AON Diagram
Figure 3. (n.d.-b). projectmanager.com. https://www.projectmanager.com/wp-content/uploads/2021/05/Activity-on-Node-Image.png
A quick look at AON diagrams (also known as PDM diagrams, for the Precedence Diagramming Method) reveals the difference between them and AOA diagrams: In AON, nodes represent activities or tasks. The IDs of tasks are written within the nodes, usually alongside their estimated durations. Arrows simply indicate the prerequisites for a task, as well as the "path" that must be followed to complete it.[3]
What's the difference?
Ah, the golden question. At first glance, whether you're using Activity on Node diagrams or Activity on Arrow diagrams, you're still getting the same point across, right? Chances are you already thought about which one you prefer, off of visual style alone.
Well, it turns out there is a difference.
AON diagrams are typically used to highlight the relationships between tasks, whereas AOA diagrams are usually used to shed light on the flow of the project as a whole or in sections.
What type of diagram should I use?
AON diagrams help highlight the relationships between tasks. This gives project managers a lot of flexibility for managing larger projects because they can easily see the dependencies of nodes. (We'll talk more about them in just a bit.) These dependencies can show project managers where bottlenecks lie, and how they can optimize their game plan to tackle development.
AOA, on the contrary, is a bit more straightforward. It quickly shows project managers where constraints lie, which tasks are more like outliers, and which are thickly tangled up in relationships with other tasks. It can be used to separate the development schedule of a project up into major milestones based on tasks and determine which phases of the development process will be the most complex and involved.
Which type you should use depends on the type of project you're working on and the size of your team, but hopefully, the information above will give you a good place to start.
Dependencies and you
The example diagrams above were pretty bare-bones, only including minimal information. However, project schedule network diagrams can also include elements such as dependencies.
Dependencies are simple, two-letter codes meant to highlight the relationship between successive tasks in a network diagram, and as stated before are mostly used in AON diagrams.
Dependency types
There are four types of dependencies. [4]
FF - Finish to Finish
FS - Finish to Start
SS - Start to Start
SF - Start to Finish
In dependencies, the first letter indicates what status the predecessor task needs to achieve before the succeeding task can achieve the status signified by the second letter.
In simple terms:
Finish to Finish - Predecessor must be completed to complete the successor.
Finish to Start - Predecessor must be completed before the successor can be started.
Start to Start - Predecessor must be started before the successor can be started.
Start to Finish - Predecessor must be started before the successor can be finished.
Well, that's all!
That was a mouthful! But hopefully, you were able to digest it all. Let's take a look at the example network diagram you saw at the beginning of this post. You should now be able to interpret it!
Figure 1. (n.d.-b). Project-Managemant.info. https://project-management.info/project-schedule-network-diagram/
Do you know whether this diagram is AON or AOA? Remember what the dependencies mean? If you've been paying attention, you shouldn't have any trouble. So get out there and get ready to use this powerful tool to help visualize your own projects!
References
[1] Network diagrams in project management — definition, types, and ... (n.d.). https://business.adobe.com/blog/basics/project-network-diagram
[2] Sebastian. (2023, August 19). Project Schedule Network Diagram: Definition: Uses: Example. Project. https://project-management.info/project-schedule-network-diagram/
[3] Sebastian. (2021, February 20). PDM - precedence diagramming method [FS, FF, SS, SF] (+ example). Project. https://project-management.info/pdm-precedence-diagramming-method/
[4] crm_org. (2024, January 25). What is a network diagram in project management? (examples included). CRM.org. https://crm.org/news/network-diagram-project-management
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