Software Product Line Engineering is a recent approach of software engineering. It gathers activities of development of a set of software belonging to a particular domain. The main goal of this approach is to increase the productivity and to decrease the time-to-market. One of the main difficulties for representing software product lines is variability management, ie taking into account common and variable parts of products. This paper proposes a new approach for modeling product lines with UML integrating functional, static and dynamic aspects. First, an extension to use cases, class diagrams and sequence diagrams is proposed. The coherence between parts of the product line models is then ensured by OCL (Object Constraint Language) constraints.