Existing multimedia document models like HTML, MHEG, SMIL, and HyTime lack appropriate modeling primitives to fit the needs of next generation multimedia applications which bring up requirements like reusability of multimedia content in different presentations and contexts, and adaptation to user preferences. In this paper, we motivate and present new requirements stemming from advanced multimedia applications and the resulting consequences for multimedia document models. Along these

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... s, we discuss HTML, HyTime, MHEG, SMIL, and Z Y X, a new model that has been developed with special focus on reusability and adaptation. The analysis and comparison of the models show the limitations of existing models, point the way to the need for new flexible multimedia document models, and throw light on the many implications on authoring systems, multimedia content management, and presentation.