UML comes from Unified Modelling Language. Is a visual language that prove useful to communicate relationships between concepts in the software world. Example of concepts are: contexts, containers, components, classes. Examples of relationships are: is-a, has-a, inherits, calls, method return, depends-on, installed-on.

UML failed to become a fully formal language and now is widely used as a micro-language used to communicate better.

There are several types of useful UML diagrams each of them focused on some aspects:

• Class diagrams - shows classes and the relationship between them: is-a, has-a, uses, aggregates
• Sequence diagrams - shows the order in which control is passed from component to component
• Deployment diagrams - used to describe what containers exists and how they are contained in others and how they communicate between them: hosts, ips, ports, protocols, endpoints.

To remember them use the UML cheatsheet. To learn UML just read this small (200 pages book): Martin Folwer - UML Distilled - pdf

Tools

• ObjectAID - lightweight eclipse plugin to generate diagrams from existing java sources - http://www.objectaid.com/
  • class diagrams (free version)
  • sequence diagrams (paid version)
• https://www.quora.com/What-is-the-best-UML-plugin-for-Eclipse
  • papyrus - http://www.eclipse.org/papyrus/download.html
  • Obeo UML Designer 2 - based on syrius
    • http://www.umldesigner.org/ref-doc/define-the-application.html#deployment-diagram
    • http://marketplace.obeonetwork.com/module/uml
  • sirius eclipse framework - http://www.eclipse.org/sirius/overview.html

Resources

• UML cheatsheet - http://loufranco.com/wp-content/uploads/2012/11/cheatsheet.pdf
• read first UML Distilled - http://ce.sharif.edu/courses/96-97/1/ce418-1/resources/root/Books/UMLDistilled.pdf
• generic (quora/stackoverflow/google)
  • quora - https://www.quora.com/What-are-the-best-sources-to-learn-UML