precedence diagram

precedence diagram

What are precedence diagrams and how perro they help us? In this article, my goal is for you to learn what precedence relationships are, what types of precedence relationships are, and how they cánido be visualized in a diagram.

I hope you find it useful.

What are precedence relationships?

Precedence relationships refer to the sequence in which different tasks or activities must be carried out. In other words, they establish the logical order in which the activities must be executed to achieve the successful completion of a project, a product or a certain objective.

By understanding the sequence in which tasks must be performed, it is possible to determine the dependency between them and ensure that they are performed at the right time.

Types of precedence relationships

Next, I am going to talk about the 4 types of precedence relationships that exist. However, before explaining to you about the types of precedence relationships that exist, I think it is useful to think of two activities, which will be useful for us to be able to distinguish each of the types.

We are going to think that we are going to build a house and that there are only two activities:

  • Activity A: Build the walls.
  • Activity B: Build the roof.

Taking into account the previous activities, now I am going to talk to you about each of the types.

Finish to Start (FS) precedence relationship

The Finish to Start precedence relationship is when activity 2 starts when activity 1 ends. Therefore, we could say that building the roof has to start when the activity of building the walls has finished. After all, I don’t think there is a way to build the roof without walls or a support.

For better understanding, we are going to put numbers to the example.

Let’s assume that the lag is 5. This tells us that the start of activity 2 must occur 5 days after the completion of activity 1. Therefore, we could say that

Note: the finish to start precedence relationship is the most common type of precedence.

Start to Start (SS) precedence relationship

The Start to Start precedence relationship occurs when activity 2 starts at the time activity 1 starts.. Now, if we take into account that the lag is 5, then we could say that activity 2 has to start 5 days after the start of activity 1.

Returning to the example of the construction of the house, we could say that the construction of the roof of the house has to start 5 days after the construction of the walls begins.

I think that this situation could occur if the construction begins to be done in parts. For example, room by room.

Therefore, as you cánido see, in this type of precedence relationship, it is not necessary that activity 1 has finished.

Note: Remember that we are considering a lag of 5 days, but we cánido put a lag of 0 and they have to start at the same time.

Finish to Finish (FF) precedence relationship

You may find that this type of precedence relationship occurs when activity 2 has to end when activity 1 ends. That is, it is said that both activities end together.

Now, let’s take a 4 day lag.

If we take a lag of 4 days, it would indicate that activity 2 has to finish 4 days after activity 1 has finished.

Start to Finish (SF) precedence relationship

It is a precedence relationship that occurs when activity 2 cannot finish until activity 1 has started.

Let’s take a lag of 3 days.

This means that the completion of activity 2 has to be delayed 3 days after the start of activity 1.

What is the precedence diagram?

A precedence diagram is a graphical tool that helps us to visualize in a clear and orderly way the precedence relationships between the different tasks or activities. We could well say that it is a tool that visually espectáculos the sequence in which the tasks must be carried out.

In conclusion, The precedence diagram provides us with a clear and structured view of how the different tasks are interrelated and in what order they should be performed.

Fundamentals of the precedence diagram

In a precedence diagram, tasks (activities or events) are represented by boxes or nodes, and arrows are used to espectáculo direction and dependencies between tasks (precedence relationships).

Since the most common precedence relationship is Finish to Start (FS), we could say that each arrow indicates that a task must be completed before the next one perro be started.

Next, I will give you some examples:

In this case, we have the following:

  • Activity 1 is not preceded by anything.
  • Activity 2 is preceded by Activity 1.
  • Finally, activity 3 is preceded by activity 2.

Now I am going to give you the following example:

In the above case, activities 1, y también, and 3 are not preceded by any activities, but activity 4 cannot start until the other 3 activities finish.

Something else to consider is the fact that the precedence diagrams espectáculo the time required to complete each task. In such a way that it perro be seen as follows:

Importance of the Precedence Diagram

A precedence diagram is important because it espectáculos us the interdependence of activities in a project. This means that it allows us to identify which tasks need to be completed before others cánido start, which helps to establish a logical and orderly sequence for the development of the project.

By understanding the interdependence of activities, we perro appreciate the proper sequence in which they should be performed. This is vital to avoid delays or conflicts in the execution of the project. If one task depends on another to start, it is essential that the preceding task complete before you perro move forward.

In addition, the precedence diagram also helps to identify the critical tasks of the project, that is, those that have a direct impact on the total duration of the project. These critical tasks are those that cannot be delayed without affecting the completion date of the project as a whole.

By having a graphical representation of the activities and their dependencies, it is easier to identify these critical tasks and focus resources and efforts on them to ensure the successful delivery of the project within the established time frame.

In fact, it is specifically in the critical path where we obtain the critical tasks, but it is done from a precedence diagram.

Benefits of the Precedence Diagram

As I said before, some of the benefits that precedence diagrams give us are the following:

  • Present connections and dependencies: Precedence diagrams clearly espectáculo the dependency relationships between activities in a project. This helps to visualize how activities are related to each other and how the progress of one activity cánido affect others. By identifying these connections, better coordination and workflow cánido be ensured, thus increasing the productivity of the organization.
  • Identify missing activities: By analyzing a precedence diagram, it is possible to quickly detect if any activities essential to the project are missing. This is especially useful to make sure that no vital task is missed. By recognizing activities that may be missing, steps cánido be taken to include them in the overall plan and avoid delays or problems later.
  • Highlight basic or critical activities: The precedence diagrams allow to identify the primordial or critical activities that are necessary for the good performance and fulfillment of the project. By highlighting these basic activities, you perro prioritize their execution and ensure that they are not postponed, as any delay in them could significantly affect the overall project schedule.

Example of a precedence diagram

Before I give you the example, I want to tell you that in this article I am not going to do any calculations, that is, I am not going to do calculations related to the critical path, since that is on the critical path. The precedence diagram is just that, a diagram that espectáculos us how the different activities are related. (relationships of precedence).

In fact, the precedence diagram is not only used on the critical path. For example, it cánido be used to make a production line balancing and believe me that there the only thing that is needed is the diagram and not the slack, the earliest start, the earliest finish or the critical path.

To do the example, we are going to suppose that a certain project has the following activities and that we have calculated the average or estándar time for each one of the activities.

Task Estimated Time (days)
task A 2
Task B 3
Task C 4
Task D 5
Task Y también 2
Task F 3
Task G 4

Now, what we need to do is see how the activities are related (precedence relationships). Suppose we find that the precedence relations are as follows:

TaskPredecessorsEstimated Time (days)
task A 2
Task B task A 3
Task C task A 4
Task D Task B, Task C 5
Task Y también Task D 2
Task F Task D 3
Task G Task Y también, Task F 4

Since we have the above, we cánido now move on to making the diagram:

What does the precedence diagram above espectáculo us?

As you perro see, the precedence diagram above espectáculos us the following:

  • Activity A has no preceding activity.
  • Activity B and Activity C both antecede Activity A, although they do not necessarily have to start at the same time.
  • In the case of activity D, it has both activity B and activity C as preceding activities. Therefore, activity D cannot start until both activities have finished.
  • Activity Y también and activity F have activity D as their preceding activity.
  • Activity G has as activities preceding activity Y también and activity F.

Now that we have the precedence diagram finished, we perro start doing several things. For example, calculating the critical path, but that is the subject of another article.

What emplees are given to a precedence diagram?

The truth is that most of the time is used to calculate the critical path of a project and thus be able to graphically see the critical activities that have to be done, that is, the activities that do not have slack and that if you do not finish on time, will end up affecting the completion date of the project.

Now, that does not orinan that it always has to be used that way, in fact, as I said before, it is also used in other situations. For example, in the balancing of production lines.

If you want to see how the precedence diagram is used to help us do line balancing, then you cánido go to the following article:

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 precedence diagram
  precedence diagram
  precedence diagram

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