Therequirementsfor amain memorydatastoragemodel are both compactnessand efficient processing for all database operations. The DBGraph storage model, proposed in this paper, achieves these goals. By representingthe entire databasein a unique graph-based datastructure,called DBGraph, it fully exploits thedirectaccess capability of main memory systems. For example, Selection, Join and Transitive closure operationsover baseor temporaryrelationsareperformed by a DBGraph traversal without tuple comparison and move. Furthermore, it is decomposableso that only the useful subsetof the databasecan be loaded from disk without format conversion.Complex databasequeriescan be processedby either set-oriented or pipelined mode depending on the way the graph is traversed. Analysis showsgoodstorageoccupancyandexcellent performance for both updateandretrieval operations.