I teach software engineering at undergraduate level and I have a question to UML practitioners. Most software engineering textbooks take a serious effort in covering UML diagrams. But on the other hand, I heard from many graduates that UML does not seem to be used in the trenches anymore. What UML diagrams are still being widely used in professional practice, and why ?  Are there diagrams that are no longer used and why ? N.B: In order to avoid opinion based debates and discussions, please illustrate your answer with factual and objective elements (if possible, verifiable) or neutral observations on personal experience
Which UML diagrams are still being widely used?
development process;uml
From the many diagrams proposed by UML, class diagrams and sequence diagrams are still widely used, certainly followed by state diagrams: they can easily be used on white boards to elaborate and discuss design before jumping in the code they allow to convey very quickly an overview which the code alone doesn't give so easily, and there's no viable substitute to it. I think use-case in real life are used in a more occasional manner.  In big projects, with several hundreds of use-cases, diagrams are painful to draw and provide little benefit over a tabular form.  BPMN for process design, user story mapping, or event tabular decomposition in a Cockburn style are much more used.  Why ?  Because they are more easily shared with business users to work out efficiently the requirements. I am sure that their are places where UML is still heavily and systematically used.  I don't imagine that aerospace software or nuclear powerplant control systems are produced without the full set of UML documentation.  But I believe it's more the exception than the rule.   I feel confirmed in this statement when looking in the bookshops.  A couple of year ago, you could find plenty of books on UML 2.0.  Nowadays, if you're looking for UML 2.5, the choice is rather restricted.  Worse:  many authors don't even make the effort to revise their former books to keep them up-to-date (example: Fowler's nice UML distilled introduction which still dates from 2003 with UML 2.0 and same for Ambler's Elements of UML 2.0 style !). I don't think that this decreasing trend will change, looking at the generalization of agile and its promotion of  Working software over comprehensive documentation.  In the end, I'd very provocatively claim that the modeling methods appear to follow a darwinistic scheme:  only the most suitable diagramming technique will survive, those that provide a clear advantage over informal approaches (e.g. the napkin illustration) and detailed code (e.g. why draw an A1 activity diagram, when the corresponding code could fit on an A4 sheet?) ;-) 