The Eventa entity is used to represent a record of an event, as recorded in the Reference statements. The roles in the eventa are carried out by the Persona who are linked to the Eventa by the EventaPersona record. The Persona, Dates and Places which are linked to the Eventas also linked to to the same Reference document.
The Event entity, by contrast, represents the actual event we believe occured, these are linked by the EventEventa record. Both the Eventa and Event share the same group catorgories, types and roles, as described in the Event Type subsystem. The link between these records is further explored in the Event - Eventa overview page.