We developed a SMIL-based collaborative multimedia authoring tool supporting a mechanism for conceptually representing the temporal relations between different media. Among the many editors that make up our system, the temporal relation editor provides users with an intuitive mechanism for representing the conceptual flow of a presentation by simple and direct graphical manipulations. Our system proposes TRN (Temporal Relation Network) as its internal multimedia presentation representation. The TRN corresponds exactly to the conceptual temporal structure of the multimedia presentation. A TRN is composed of media objects, delay objects and a set of temporal relationships among objects. A media object is associated with a duration. A parallel relationship found in a TRN can be collapsed into a single par (parallel) synchronization block. This collapsible synchronization block facilitates the determination of the playing time of each component and can be the basic unit for reusability o...