Notification Stream

The Notification Stream operator takes a relation as input, and outputs a stream that consists of events whose presence is determined by a specific time interval.

Assume that the following conditions are true:

• The time interval of the Notification Stream operator is set to 1 minute.

• An event arrives at the input relation at 2:00 in the afternoon.

If the event is still in the relation at 2:01 in the afternoon, then the event is included in the output stream for the first time.

If the event is still in the relation at 2:02 in the afternoon, then the event is included in the output stream for the second time.

If the event is still in the relation at 2:03 in the afternoon, then the event is included in the output stream for the third time.

If the event is no longer in the relation at 2:04 in the afternoon, then the event is no longer included in the output stream.

The scenario in Gap Window involves creating a relation that indicates which message is missing at any point in time. You could use the Notification Stream operator to create an output stream of resend requests for the missing messages. Connect the Gap Window operator to a Notification Stream operator, configure the time interval, and then send the output to a Stream Output operator.

To Create a Notification Stream Operator

1. Drag a Notification Stream operator from the Palette to the Design view.

2. Connect the input of the new Notification Stream component to an operator that has relation output.

3. Double-click the Notification Stream operator.

   The property editor opens. Notice that the component has inherited the schema of its input relation.

4. Use the Notify Every field and drop-down list to specify the time interval.

5. (Optional) Click the Documentation tab and supply notes on this component.

6. Click OK.