If you need a quick reference guide for the UML notation, check one of the following great UML cheat sheets (in no particular order, though the last one if my preferred one):
- Visual Studio UML Reference. It includes activity, component, class, sequence and use case diagrams (menu on the left). The only thing that should be improved is that the name of the elements is not shown directly in the diagram but explained in tables below. Curiously enough, this UML reference sheet is part of the Visual Studio 15 documentation as the UML designer was removed from later versions of Visual Studio.
- Lou Franco UML Cheatsheet. To the point. Example diagrams annotated with the name of the modeling elements used in the example. Class, use case and sequence diagrams covered
- Practical UML Reference by Embarcadero: Very complete, even covering component and deployment diagrams (which is not the case for most of the previous ones). It used to include self-tests to quickly check your knowledge of the notation but this part seems to have been removed from the site.
- UML Diagrams: Detailed overview of all UML diagrams (including the new features of latest UML versions). It’s more a reference guide than a cheatsheet though, since each diagram has its own dedicated page. It is updated to reflect the UML 2.5 version.
- UML Notation summary for class diagrams and sequence diagrams. I include it as I like the minimal “semantic” description regarding association cardianlities and the distinction between composition and aggregation.
- UML reference sheet from the National University of Singapore. It covers all diagrams, some in more detail than others. There are no explanations, so it’s more of a notation reminder.
- Allen Holub’s Quick UML reference. Lots of examples to help you understand each notation element, including code examples of how some aspects would be expressed in Java for those with a programming background that may find this “mapping” useful to understand the concepts.
Some are quite old, but I still like them and the main elements of the UML notation have not changed a lot during all these years (except for the interpretation of the includes and extends relationships in use case diagrams; you should be careful with this).
And if you want to learn more than simple notation details and go deeper in your understanding of your UML language, our selection of UML books may be helpful as well (and you can also play with some of the UML tools we recommend).