The timeline shows events in people’s lives such as their birth, death, starting school, etc. In the table of people, it has the person’s name, the id number of their father, the date of their birth, and the date of their birth. In the events table, it has other events in their life.
So, if there’s an entry on the people table like this, ‘id=2, name=“Adam”, father=1, birth=25, bref=“1901 Census”, death=75, dref=“Death Certificate”’, it would indicate that the father was the person with the id 1 and they were 25 when Adam was born, the information was found in the 1901 Census, and Adam died when he was 75 and that information was taken from his death certificate.
If there was an entry in the events table like this, ‘id=1, event=“Graduated from Harvard”, date=24, relative=2, dref=“Photograph”’, it would indicate that Adam (relative refers to the id of the person the event relates to) graduated from Harvard when he was 24, and this information is based on a photograph of the graduation that has something like ‘Adam aged 24’ written on the back.
The code calculates the date based on the ages given and plots them on the timeline of the family history.