In this paper, we discuss important issues in designing and implementing a multimedia database system. First, we describe features used to model the content of image, video and music data. Based on the object model, we propose a multimedia framework and an object-level spatial/temporal model to represent the spatial/temporal relationships between media objects. Three new types of aggregation relationships composed of composition, temporal, and spatial relationships are considered in the framework. To support content-based retrieval, we propose a multimedia query language and two kinds of query interfaces for users to specify content-based queries. Finally, two kinds of multimedia query processing techniques are addressed.