Lately, I’ve been having trouble with UML Sequence Diagrams. So, I decided to do further research to better understand the subject.

Due to learning about it in class, I have some prior knowledge about the subject. First, there’s the actor which is usually represented by a stick figure. The actor essentially acts as a user stand in. The rest of the classes are participants. Think of them as a path the actor has to walk across. The diagram shows the path that the code takes when the user executes the code.

I used this article for reference: Sequence Diagrams – Unified Modeling Language (UML) – GeeksforGeeks

It’s a beginner’s guide to UML sequence diagrams. It defines an UML sequence diagram and all vocabulary associated with it. It then informs how to one and the pros and cons of using one.

The first thing I started to better grasp was lifelines. I used to think lifelines were the solid lines but they depict an individual participant. Lifelines represent each instance in a sequence diagram. They are displayed in rectangles and go by their name and type. They are similar to actors but portrays objects internal to the system.

I also learned more about the messages. I knew that solid lines output messages and dashed lines returned them. I didn’t know that a solid line and a dotted represent synchronous messages and a single dotted line represent asynchronous ones. Synchronous messages wait for a reply before the interaction can move forward. Imagine if to people were moving boxes to a truck. Person A hands a box to Person B who puts it the truck. Person A must wait until Person B signals that they are done with their task. On the other hand, asynchronous messages don’t need to wait for a reply so Person A would just hand Person B the box without waiting for a signal.

So, to summarize what I learned. the diagrams are just a different way to demonstrate the code. It’s a communication tool between developers, managers, stakeholders, project managers and clients. It’s like a blueprint that anyone can look over. Clients can look over the plans without getting confused and make edits if necessary. Developers can take the blueprint and convert it into actual code. UML diagrams contain an actor that takes the role of a user engaging with the code. The participants represent the rest of the classes. The vertical rectangles represent the duration of a class’s execution. The arrows, not participants as previously mentioned, represent the path the code takes. Think about everything as components of a map.

Overall, this further research deepened my understanding of UML sequence diagrams. I feel like this would help me with the homework assignment but unfortunately it didn’t answer all my questions.

From the blog CS@Worcester – My Journey through Comp Sci by Joanna Presume and used with permission of the author. All other rights reserved by the author.