The Telex middleware facilitates the design of collaborative applications in a mobile environment. It provides optimistic replication, tentative execution and disconnected work. It solves conflicts based on semantic information provided by applications. We study in particular a Shared Calendar (SC) application, whereby mobile users can create and manage meetings in a collection of shared calendars. The application provides Telex with objects representing (1) meeting creation and modification operations (actions), (2) dependence or conflict information between actions (constraints). When a conflict occurs, Telex proposes solutions to users. The advantage of this approach is a clean separation of concerns. The SC application writer concentrates on application logic, whereas Telex takes care of replication, consistency, conflicts, and commitment across all applications.