The Relation Output operator sends out groups of tuples that reflect changes in the relation result. Whenever an event triggers a change in the relation result, the Relation Output operator sends out records with a tag on the end, which indicate a + or - (records added or deleted, respectively.)
If a change occurs as a result of the triggering event such that a record changes, the IEP sends a delete record matching the changed record.
The IEP feature sends an add record out when there is an updated or new version of that record. The operator only sends events when there are change events rather than repeatedly sending the entire result.
However, if a triggering event enters into the IEP process, but the result of the final relation from that event does not change, the relation output is not triggered and the Relation Output operator does not send data.
To create a Relation Output operator: