CEP cannot detect multi event with same timestamp?

Question

When I used CEP in Flink, I found a very interesting thing is there is only one event for a time.

For example, the DataStream that I used comes from a WindowStream, because it may update the occurrences of a same event, it will generates something like this: (Event1, 2), (Event1, 3), (Event2, 1)......

When i try to select the result of applying a pattern to this output DataStream, I found for that there is only (Event1, 2), (Event2, 1)....

Can somebody give me some clues why? It's the problem of design of pattern or Flink works like this way ?

Answer 1

I found the answer. This is because:

The CEP library assumes correctness of the watermark when working in event time.

The details is in the Handling Lateness in Event Time / Fink doc