Developing a triggering system for real-time databases in distributed environment

MMDB (main memory-resident database) systems have been used for real time applications, such as a stock market and an auction system, which require fast response time and predictable behavior. However, most existing MMDB systems do not support active functionalities. Also, the trigger capability which is specified in SQL3 and implemented in some conventional DBMSs provides only an extremely limited form of active functions. The paper proposes a scheme to add active capabilities to existing MMDB without modifying the kernel. Generally, active functions can be classified into event-triggered active functions, such as decision of buying or selling point according to the state of database, and time-triggered active functions, such as periodic updates of stock prices, which are frequently used in real time applications. The proposed scheme is designed to provide both kinds of active functions for MMDB by putting a time manager which checks an absolute time far a time trigger and an SQL processing module which provides an event trigger.