Precedence Diagramming Method (PDM) Explained

Project management is becoming more demanding as scale and scope become larger and more complex. Multiple teams, vendors, partners, and stakeholders contribute crucial inputs and results to successful projects. 

Let's take a web design project in a creative agency as an example. A standard project may involve web and graphic designers, front-end developers, copywriters, marketing strategists, and project managers. The team may be working across several time zones and continents, making work dynamics even more complex.

Using proper techniques and assistive tools is worthwhile in developing good project management practices. The precedence diagramming method (PDM) is one such assistive tool. This article explains what is PDM in project management. We'll share an example and show how project management software can help project managers use PDM to plan successful projects. 

What is PDM in project management?

The precedence diagramming method (PDM) is a graphical tool used for scheduling activities in a project plan. PDM maps out project development by creating a visual representation of critical paths and dependencies.

The primary output of PDM is a project schedule network diagram. The project schedule network diagram is an input in new projects' "develop schedule" process. Precedence diagramming uses nodes to represent activities and links them with lines and arrows illustrating paths and dependencies. It's a quick and easy visual scheduling tool for project managers.

Precedence Diagramming Method (PDM) advantages

You gain many benefits from using PDM. Some advantages are:

  • Precedence diagramming method (PDM) helps project managers define a clear and proper sequence of project tasks and activities
  • PDM highlights paths, relationships, and dependencies between activities to ensure successful delivery 
  • PDM helps teams know their priorities and assignments at a glance
  • PDM serves as a visual communication and project update tool for project managers, teams, and stakeholders
  • PDM helps identify missing activities and develop an accurate project schedule

Precedence diagramming method example

Every precedence diagramming method example must include activities, durations, and dates. The project manager starts by identifying activities with a critical path and finding and connecting dependencies to ensure the workflow is ordered optimally. 

There are four ways to illustrate a project schedule network diagram. These form the connection between activities in a precedence diagram. They are:

  • Finish-to-Start (FS): In this case, task B cannot start until task A has been completed
  • Start-to-Start (SS): In this case, task B cannot start until task A starts
  • Finish-to-Finish (FF): In this case, task A cannot be completed until task B is completed
  • Start-to-Finish (SF): In this case, task B cannot be completed until task A starts

It is possible to have projects where all activities are independent of one another. Typically though, most projects fall under one of the four cases above. 

How to implement precedence diagramming software

Implementing precedence diagramming software is easier than it sounds. You can use online tools like diagrams.net or Edraw to draw precedence diagrams and share them with teams and stakeholders easily. 

You may have to download an app or software package and follow the steps to create your precedence diagram. Most precedence diagramming software allows you to choose from various shapes, forms, and grids. You can also color code and number your nodes according to the criteria for your precedence diagram. Now you're ready to save, share, and reuse it as a template for your next similar project. 

Is a precedence diagram better than a Gantt chart?

Precedence diagrams and Gantt charts visually represent project schedules. Gantt charts show the schedules interspersed on a timeline, while precedence diagrams use network diagrams to show a project's tasks and how they connect. 

Both scheduling methods show who's responsible for scheduled activities and the workflows necessary to complete them. Gantt charts are straightforward with activities listed in a spreadsheet fashion, whereas precedence diagramming is more visual with nodes (or boxes) and arrows showing the sequential order of tasks.

Neither approach is better than the other. They both shine in different cases. Project managers must determine the more appropriate method depending on the project phase and how they share and communicate reports and project progress with involved stakeholders. 

Gantt charts are useful for managing tasks and timelines during ongoing projects, while precedence diagrams are more valuable in project planning.

How to create a precedence diagram with Wrike

Wrike organizes project plans and schedules to help you draw precedence diagrams quickly. First, define all the tasks needed to complete the project. Then, look at each task to check if they fall into the critical path or have dependencies. 

Organize activities in the precedence diagram by assigning due dates and durations. Once your data is organized and accessible, you can input it into PDM software to draw a project schedule network diagram. 

Are you looking for a tool to help you organize and schedule your projects better? Look no further. Get started with a two-week free trial of Wrike today.

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