What You Need To Know About The Four Precedence Diagramming Methods (PDM)
The 3rd step of the 7 main processes in project time management is called Sequence Activities, which is the process of pinpointing and documenting connections among the project activities, and the fundamental result of this process is Network Diagram.
In the course of the Sequence Activities process, the actions described during the Define Activities process are sequenced, since some of them will rely on each other. A Network diagram depicts the activities with boxes, portraying the correlation of activities.
The Precedence Diagramming Method is one of the multiple ways you can use to make network diagrams. Inherently, you can assume there are some connections and dependencies amidst some activities in the PDM.
There is a big portion of questions related to the Time Management knowledge area in the Project Management Professional certificate exam, so signing up for any project management training or course that can provide you with all of the detailed information you need to understand the relationships in the process and adding them to your study plan is a great idea.
For now, if you want to learn more about the kinds of relations in PDM (Precedence Diagramming Method), continue reading this blog that will tell you all about it, and provide you with some precedence diagram method examples to make it easier to understand.
Network Diagrams And Precedence Diagramming Method
There are four relationships among the activities you go through with the Precedence Diagramming Method that have to be conducted to achieve the network diagram of a project. These are: Finish to Start, Start to Start, Finish to Finish, and Start to Finish.
Now we’re going to take a look at each of them.
Finish To Start (FS)
Finish To Start is the first and most regularly used dependency between activities and is often referred to as FS.
When an activity isn’t able to get started unless another activity before it ends, that means a finish to start dependency had to be placed in the middle of these two activities.
To make it clearer, some good examples of finish-to-start dependencies could be when you’re building a house and you can’t place the floors and wallpapers before you finish constructing the foundation. Basically, if you’re creating something, you cannot polish the details and add all the extra functions until you have the bare bones completely solid.
Start To Start (SS)
Start to Start is the second kind of dependency and it is often written as SS. Start to Start is quite simple to understand, it just means two activities that begin at the same time. One example of a Start to Start activity would be mixing the ingredients for a cake at the same time you preheat the oven. While making a network diagram, those two activities would be added next to each other.
Finish To Finish (FF)
Finish to Finish is the third type of dependency commonly referred to as FF. Just like with Start to Start, Finish to Finish is very easy to understand, it indicates two activities that will end at the same time.
A good example of a Finish to Finish activity would be a design that cannot be completed until all of the chances are accepted by the client and are being worked on at the same time.
Start To Finish (SF)
The fourth and last type of dependency in PDM is called Start to Finish, usually abbreviated just SF, and the least commonly used dependency in projects.
To put it simply, Start to Finish means one activity can only be completed after another one begins. A good example of a Start to Finish dependency would be how a worker doing their shift cannot clock out and leave until a relief shift worker arrives, clocks in, and starts their shift. If the second worker is late, the current shift can’t finish. The first activity can only finish once the following task has started.
Let’s Talk About GERT
Graphical Evaluation and Review Technique, typically known as GERT, is an analysis technique in networks that project managers use which allows probabilistic solutions of both network logic and estimation of activity duration.
An example of GERT could be:
- Activity 2 contains an FS dependency to Activity 1
- Activity 2 can start only after Activity 1 is completed.
- Once Activity 2 is finished, Activity 1 can begin again.
The examples we gave before for each of the types of dependencies can be used for this scenario as well.
The Four Dependencies in PDM
Now that we know the kind of relationships in PDM, we can take a look at each dependency. Do you know there are four types? Here they are.
Types of Dependencies in Time Management Sequence Activities:
- Mandatory Dependency (Hard Logic): Inherent in the nature of the work. (e.g. You cannot test a product before you develop it).
- Discretionary Dependency (Preferred, Preferential or Soft Logic): Determined by the project team and can be changed in order to shorten the length of the project. (e.g. Person 1 activities order changes from a -> b to b -> a)
- External Dependency: Comes from outside of the project. (e.g. Government, Suppliers, etc.)
- Internal Dependency: Involves a precedence relationship in project activities. (e.g. You cannot start building something before the design is done.)
Let’s dissect all of the details for each of the dependencies in PDM.
Mandatory Dependency or Hard Logic
Mandatory Dependency, also known as Hard Logic, is the 1st type of dependency in PDM.
Mandatory dependency is ingrained in the essence of this work. Let’s think about a recipe a chef is developing. We know they wouldn’t be able to taste it and check for any errors before the recipe is fully finished and they actually get on preparing it. So, in this case, we can see how there is a compulsory dependency between the development of the recipe and testing the final product.
Discretionary Dependency or Soft Logic
Discretionary Dependency, also known as Soft Logic, is the 2nd type of dependency in PDM.
This dependency is defined by the team working on the project and can be subjected to modifications to make the project’s timeline shorter.
A good example would be, if there are several activities that someone needs to complete so they can finish off the project, these can be changed around and modified in a way that would fit better and make it flow faster.
External Dependency is the 3rd type of dependency in PDM.
As the name indicates, external dependencies usually come from outside of the project.
An example of this dependency in the Precedence Diagramming Method would be how you need to finish another project so you can get a new one started. Basically, if there is something that you need to do that is external to the project you want to start in order to be able to do so, that is an external dependency.
Internal Dependency is the 4th type of dependency in PDM.
Internal Dependency refers to any relationship between activities that are happening inside of your project, with one of the two being incapable of starting because the other one hasn’t been completed yet. Just like with external dependency, there is an activity that has to be completed before another one starts, but in this case, both of them are inside of the same project.
For example, you cannot start production of a garment you want to make before the designers are finished. This is a type of internal dependency in the Precedence Diagramming Method.