Windows and punctuation
Windows and punctuation are used to logically group tuples and provide informative signals within a stream.
A window is a finite sequence of tuples within a stream. Examples of windows include the last five seconds of tuples and the last 100 tuples.
Punctuation is a control signal within a stream that either creates boundaries within a stream of tuples (window punctuation marks) or identifies the end of a finite stream (final punctuation marks).