As a general rule, events are things that happen on a specific date. Use the dateRange form to indicate that an event took place at some time between 2 dates. In most cases, a DatePeriod is inappropriate for an event; if the subject of your recording occurred over a period of time, then it is probably not an event, but rather an attribute.
Event structures can be used to record notes about an event without asserting the event actually occurred. An event structure asserts the event did occur if any of the following are true:
There is a DATE substructure
Version 5.4 (1995) introduced the “event did occur” meaning of event.DATE, so it is now well-established in applications and files. However, it is common for users to enter a date range with no end without intending to indicate that the event occurred. For example, pre 7.0 files sometimes used
to mean what 7.0 encodes as
without intending to imply that NATU ever did actually occur. Because this is a “sometimes used” rather than a “formally means” situation, it is likely that data using 5.x “after meaning not before” de facto pattern will be transferred as-is into 7.0 and persist in files for the foreseeable future.
There is a PLAC substructure
The event has a payload. A special payload Y can be used with some event types to indicate that the event is known to have occurred without providing any additional information about it.
If none of the above are true, the structure should be seen as a place for inconclusive research notes about the possibility of the event. An assertion that an event did not occur should be encoded using the NO structure.