UML - Communication Diagram Tutorial
Communication diagrams are a type of interaction diagram that show the same information as UML sequence diagrams. Learn the difference between communication and sequence diagrams, then see how to build the former in Lucidchart.
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Review the Basics
UML encompasses a wide range of diagrams and notation styles, so it may be helpful to revisit the basics. This page can help you understand what a sequence diagram is, and this guide to UML explains essential concepts of the Unified Modeling Language. Symbols that are present in sequence diagrams and class diagrams, including actors, objects, and messages, are also found in communication diagrams.
Finally, be sure that you understand the difference between communication and sequence diagrams. The latter chart the order in which messages are sent and received within a sequence. In contrast, communication diagrams focus on the relationships between objects—hence the name. Many shapes and symbols that are used in sequence diagrams are also suited for communication diagrams. Both can be retrofitted to fit the other's structure, because the information displayed is so similar.
SELECT A MEDIUM
Most students and professionals who encounter UML for the first time are overwhelmed. By picking the right UML tool, you'll reduce confusion and be able to share, edit, and collaborate with ease. Reserve pen and paper for other topics—communication diagrams are best viewed and altered with a full-featured computer application.
We'll proceed as though you're using Lucidchart. It's ideal for real-time collaboration and cross-platform usage, since Lucidchart is completely cloud-based.
ADD SHAPES AND LINES
Begin your diagram by opening a new document in Lucidchart, then click “More Shapes” and turn on the UML shape library. Most shapes for communication diagrams can be found in the sequence and use case diagram sections. Adding shapes to the canvas is as easy as dragging and dropping.
Many—though not all—communication diagrams include the swimlane shape. It’s found in the BPMN shape library. If you select a swimlane, double-click the header text to replace it with your own title. You can also click the information icon that hovers next to the shape in order to add extra rows or columns. Swimlanes merely separate the system into more manageable chunks, such as distinct areas for each participant.
If you don't want to use swimlanes, it's acceptable to arrange elements in a free-form way. You will probably drag out object shapes, actor shapes (representing participants in the system), and lines that represent instances of the relationships. These lines are known as links. Next to the lines, you can draw arrows to indicate messages. Messages should be labeled with a name and sequence number. The sequence number shows the reader how to move from object to object and message to message, i.e. where the diagram begins and ends.
Once all of your elements are represented and linked together, take a final pass at the document. It's important to review your work with fresh eyes—ask a trusted mentor to look at it, or rest for a day before you review. When you've verified the accuracy of your work, feel free to share!
Lucidchart was built with technical diagrams in mind. From UML to BPMN, any kind of business or software diagram can be modeled with our critically-acclaimed software. Try it for yourself!