In this paper, a generalized multimedia database data model based on MPEG-7 named G3M is proposed and formally defined. Different from those XML Database Management System (DBMS) solutions for MPEG-7 storage and retrieval, G3M analyses the MPEG-7 Multimedia Description Schemes (MDS) throughout to construct user-preferred database schemas, and the prototype system is built on extensible Object-Relational DBMSs. With the strong expressiveness of MPEG-7, G3M represents various aspects of multimedia data well. Domain knowledge for special application demand can be defined and used as references in G3M.