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):
- Lou Franco UML Cheatsheet. To the point. Example diagrams are annotated with the name of the modeling elements used in the example. Class, use case and sequence diagrams covered
- UML quick reference card. Another 1-page quick reference, great to be printed and keep close to you.
- UML Diagrams: Detailed overview of all UML diagrams (including the new features of the latest UML versions). It’s more a reference guide than a cheat sheet though, since each diagram has its own dedicated page. It is updated to reflect the UML 2.5 version.
- Embarcadero’s Practical UML guide: Complete coverage of all diagrams. It used to have also some UML self-tests but they don’t seem to be working anymore
- UML Notation summary for class diagrams and sequence diagrams. Very simple but I include it as I like the minimal “semantic” description regarding association cardinalities 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.
- Dzone UML getting started guide. All UML2 diagrams covered, with some basic explanations for the main notation elements.
- 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). As a curiosity, I used to highlight the Visual Studio UML Reference, which was rather complete but after the UML designer was removed from later versions of Visual Studio, they ended up removing it.
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 UML tools I recommend).