System for handling unsolicited messages from lower-tier controllers

摘要

In a multi-tier computer system, a database configuration message is transmitted from a cell controlling computer to a database cache computer to designate certain data items to be monitored at one or more station-level computers. The database cache computer is connected via a local area network to the station-level computers. The station-level computers monitor the data items and generate unsolicited messages containing changed states for data items which have changed over the monitoring period. The database cache computer receives the unsolicited message and interprets the data therein to update the relevant data items. The unsolicited messages are sent back periodically without the need for polling by the database cache computer. If desired, the data in the unsolicited messages can be limited to data which has changed since the last update of the relevant data items.