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

A database cache computer for connection in a factory automation system for improving communication between a user interface computer and a plurality of station-level computers located at a corresponding plurality of stations, the database cache computer comprising:

• database means for storing a database of data items collected from the plurality of station-level computers;
• first communication means coupled to the database means for communicating the data items through a first communication link to and from the user interface computer via a message including data items from a plurality of station level computers;
• second communication means coupled to the database means for collecting the data items through a second communication link from the station-level computers;
• and
• wherein an improvement comprises:
• means in the database cache computer responsive to a first message from the user interface computer to designate data items as being subject to change-of-state monitoring;
• means in the database cache computer for detecting changes in states of the designated data items collected through the second communication link from the plurality of station-level computers;
• and
• means in the database cache computer responsive to changes in the states of the designated data items collected through the second communication link from the plurality of station-level computers for assembling and transmitting an unsolicited message to the user interface computer, wherein the unsolicited message includes the changed states originating at a plurality of station-level computers for a plurality of the designated data items.