Advanced applications in fields like electronic publishing and telecooperation face the problem of handling multimedia information. Conventional database systems do not offer adequate support for storage management as they do not provide for the modelling, indexing, and manipulation of multimedia data. Database management systems need to be extended if they should be able to handle multimedia information like audio and video. In this paper we present an approach of extending the data model of an object-oriented database system by means of schedules which allow for the description of the temporal characteristics of multimedia operations as they occur when modelling time-dependent data like audio and video. First, we present a model of schedules and define the basic concepts and semantics to execute time-dependent operations. Second, we introduce the specification language as an extension to the VODAK Model Language and illustrate the concepts by examples. Finally, we briefly discuss th...