System for generating unsolicited messages on high-tier communication link in response to changed states at station-level computers

摘要

In a method for monitoring and collecting data in a multi-tier computer system, a database operation message, referred to as an "open" message is transmitted to a database cache computer with a list of data items in the database cache computer to be monitored on a change-of-state basis. The database cache computer responds by monitoring the data items and returning unsolicited "change data" messages containing only states for data items which have changed over the monitoring period. The change data messages are sent back periodically without the need for polling by a higher-level computer. The monitoring process is terminated by closing data records in the higher-level computer which generates a "close" message to the database computer to terminate the transmission of the change data messages. Also disclosed is a database cache computer and a user interface computer for carrying out the method.