This Event fires once each time the engine starts processing the dataset.
If the dataset has Linked Data it will only fire once at the start of the first record in the source dataset.
However, if the dataset is a child of another dataset, then the engine will start its processing multiple times - once for each record in the parent dataset. Therefore this Event will fire once each time the dataset starts.
OnEndMap Event
This Event fires once each time the engine finishes processing the dataset.
If the dataset has Linked Data it will only fire once at the end of the last record in the source dataset. However if the dataset is a child of another dataset, then the engine will finish its processing multiple times - once for each record in the parent dataset. Therefore this Event will fire once each time the dataset ends.