Using String Messages to Trigger Tasks
You can use string messages to trigger a task on another computer or to wait for a signal from that computer before proceeding.
For example, you have an online transaction processing system running on one computer (OLTP). Your data warehouse resides on another computer (Warehouse). Every night, shipment facts are summarized on OLTP and transferred to Warehouse. Before the transfer can take place though, Warehouse dimension tables must be updated.
Two packages are used to manage this process: Update Warehouse and Prepare Facts.
Update Warehouse runs on the Warehouse computer. When Update Warehouse starts, the Ask for Facts task sends a string message telling the OLTP computer to start summarizing shipment data. While shipment data is being summarized on the OLTP computer, the Update Dimensions task updates Warehouse dimension data. When this task is complete, the Wait for Facts task waits for a string message from the OLTP computer that says shipment data is ready. Only after this message is received does a Transform Data task move the shipment data to the Warehouse computer.
Prepare Facts runs on the OLTP computer. The Wait For Trigger task initially waits for the string message from the Ask for Facts task. On receipt, the Shipment Summary task prepares the data for transfer. When the data is ready, the Alert Warehouse task sends the message which, when received by the Wait For Facts task, tells Update Warehouse to start the transfer.
Ask For Facts and Wait For Trigger form a matched pair of Message Queue tasks. Ask For Facts sends the message and Wait For Trigger receives it. Alert Warehouse and Wait For Facts form another such matched pair. Their configuration differs from the first only in the text of the message.
Configuring the Ask For Facts Task
Ask For Facts sends the message "Summarize shipments" to a queue, where it can later be read by the Wait For Trigger task.
To configure the Ask For Facts task