Explain Decision and Merge Node in Activity Diagram

In the next video, you will learn the concept of a decision node.

In the previous video, you learnt that decision nodes are used to represent decisions (if-else conditions) in the activity diagram. It has one incoming flow and multiple outgoing flows, but the flow passes through only one of those outgoing flows. The direction of an outgoing flow is decided on the basis of the guard conditions.
You also learnt about the flow final node, which is mostly used to denote the empty else condition. You can represent decision node and flow final node in the activity diagram as shown below.

Video Transcript

 We will now see how to represent decisions in an activity diagram. Typically, when we program, we tend to write false conditions if else conditions are represented using a decision node. Let's take an example. In our previous activity diagram, a user logs in, he checks his notifications and as part of the notification he makes a decision after looking at the notification, if my quantity of the product are above a threshold level or below threshold level, if my quantity is above a threshold level there there's no need to take any action. So act the flow ends there. The representation of an x symbol is actually the flow final node and the conditions that are being checked here. If the product is above threshold level, all the product is below the threshold level are commonly called as the guard conditions. So as part of the decision node, as you can see, there is one inflow and there can be multiple outflows. But please note only one of the outlook flows will be executed. It is very analogous to your if else or else if conditions and post decision node, the flow could continue. If the product is below threshold level, we continue to place an order post which the user would log out and after logout the activity ends which is represented with an activity final node. So to summarize, during the decision node we could have the guard conditions to decide your FL's condition s and there could be single inflow multiple outflows and there is a flow final node and an activity final node.

Video Recap

• Activity diagrams can be used to represent decisions.

• Decision nodes are used to represent if-else conditions.

• Guard conditions are used to check the conditions being evaluated in the decision node.

• There can be multiple outflows from the decision node, but only one will be executed.

• The decision node is similar to if-else or else-if conditions in programming.

• After the decision node, the flow could continue.

• The representation of an "x" symbol is the flow final node.

• An activity final node is used to represent the end of the activity.

• The segment explains how to use activity diagrams to represent decisions.

In the next video, you will see how to draw a decision node in draw.io.

In the previous video, you saw how to draw a decision node in draw.io. You will use it further in the sessions to draw activity diagrams.

In the next video, you will be introduced to the concept of a merge node. 

In the previous video, you learnt about merge node, which is used to merge multiple input flows into a single output flow in an activity diagram. You can represent merge node in the activity diagram as shown below.

In the next video, you will see how to draw a merge node in draw.io.

In the previous video, you shed some light on how to draw a merge node in draw.io. You will use it further in the session to draw activity diagrams.

Now you have learnt about the concept of Decision node and Merge Node and where to use them. You also learnt how to draw them in an activity diagram.