Hi Franky,
Oliver has steered you toward a good start. The main value is that Craig's work will help you get a fast grip on patterns. He also helps you get your head around the distinction between a 'thing,' the design of the thing, and the model of the thing, which are all different.
BTW: My two editions of Craig's are quite dated, so I am eagerly awaiting the new release. [Oliver, if you read this please send me a reference via PM. Craig has also bundled his book with videotapes, and at least once with coursework. Though dated, these might be worth looking into.]
Depending on what you want to know, and how much experience you come in with - not just UML, but experience in your problem domain - you might need a gentler introduction, or one oriented in another direction.
I suggest you take some time and search the EA forum. Search all the sections except Latest News and Bugs and Issues; the former is for announcements and the latter is very recent. There are several threads that deal with this. They tend to be several pages (of posts) long, so it might take a while to work through them. But you will find a lot of discussion - you might have to wade through some weighty opinion to weed it out - and a lot of good hints.
What's better, many of these hints come with a description of why a given reference would be relevant to a specific aspect or approach to UML. If you find something that lines up well with your situation you could save a lot of time.
HTH, David
