UML tutorials

www.uml.org

www.sparxsystems.com.au/uml-tutorial.html

http://uml-tutorials.trireme.com/

www.tutorialspoint.com/uml/index.htm

www.freebookcentre.net/.../Free-Uml-Books-Download.html

http://courses.softlab.ntua.gr/softeng/Tutorials/UML-Use-Cases.pdf