Over the years, there has been a confluence of concepts, tools and techniques from two diverse areas: artificial intelligence (AI) and database (DB) systems. There are several ways to integrate expert systems (ES) and database systems. This paper surveys the related literature and classifies the integrated systems into four classes: enhanced DB, enhanced ES, coupling of existing ES and DB, and expert database system. A new loose coupling approach (Simple Coupler) based on predefined SQLs is then proposed.Its system architecture and system operations are described. The Simple Coupler is compared with the DIFEAD (Dictionary Interface for Expert Systems and Databases) approach and the commercial ES shell approach on the criteria of the independence of the DB, ES, the complexities and future expansibility. This approach has great practical values because of its simplicity. Finally, this paper reports on two prototypes coupling existing systems: accounting DB & financial ES and medical history database & medical diagnosis system, respectively, in the PC window environment.