Consider a stream of video frames captured from a certain security monitoring camera:

Video (frame-number, time-stamp, one-frame-of-video-data, location_id)

The frame-number attribute here becomes the unique identifier of the video frame (a tuple in the stream). A derived relation can be computed from the above relation, for example,

weapon (frame-number, one-frame-of-video-data, type-of-weapon)

There is a multimedia dependency from video-data to type-of-weapon. The dependency relations tell us how these streams are related.