Abstract. The ConcurTaskTrees (CTT) is one of the most widely used notations for task modeling, specifically tailored for user interface model-based design. The integration of CTT with a de facto standard modeling language was already identified as an import issue, but there is no consensus about the best approach to achieve this goal. The purpose of this paper is to examine the relative strengths and weaknesses of control and data flow specification in UML 2.0 Activity Diagrams to represent CTT semantics. The analysis is conducted by the definition of pattern-based activities for the temporal operators in CTT. Here, we propose an extension to the UML 2.0 abstract syntax that fully supports the concepts behind CTTs and provides an adapted graphical notation for an UML like representation.