UML basics: An introduction to the Unified Modeling Language
http://www-128.ibm.com/developerworks/rational/library/769.html

This introduction to the Unified Modeling Language, or UML, provides an overview of the most important diagrams used in the visual modeling of computing programs. The article is ideal for those who have little knowledge of UML concepts, including managers as well as novice practitioners. This has been added to World Wide Web Reference Subject Tracer™ Information Blog.