In distributed multimedia applications time-dependent data streams are conveyed and processed under real-time conditions. The timely accurate activation of the stream handlers processing the data units of streams requires deriving their scheduling times from the temporal properties of the data streams and the amount of data that is processed in each activation. In this paper, we propose the activation set concept as a data access abstraction to consume sets of data units from a group of time-dependent data streams having synchronization relationships among each other. The concept supports the consumption of multiple periodic data streams of different rates as well as the integration of aperiodic streams. It is shown how scheduling times of activations are derived from the streams' temporal properties and the requested amount of data. When a stream handler is activated, data units of the streams are selected for consumption according to synchronization relationships and tolerated skew bounds. The effects of the approach on delays are discussed in the context of a rate-monotonic scheduling algorithm. The concept provides a configurable interface to groups of time-dependent data streams which, for example, is required when mixing streams. It is widely applicable in multimedia system architectures that allow for configuration of distributed multimedia applications based on interconnected stream handling components.