Multimedia applications usually involve a large number of multimedia objects (texts, images, sounds etc.). Spatial and temporal relationships among these objects should be efficiently supported and retrieved within a multimedia authoring tool. In this paper we present several spatial, temporal and spatio-temporal relationships of interest and propose efficient indexing schemes, based on multidimensional (spatial) data structures, for large multimedia applications that involve thousands of objects. Evaluation models of the proposed schemes are also presented as well as hints for the selection of the most appropriate one, according to the multimedia author's requirements.