Lots of relational algebra mumbo-jumbo with Greek letters. Caveperson alternative is the Structured Query Language (SQL):

create table reservations (
      flight_number    integer,
      departure_time   datetime,
      passenger_name   string
);

-- how many folks are on one flight?
select count(*)
from reservations
where flight_number = 37
and departure_time = '2003-02-21 15:00'

• no place to store capacity of the plane that is being used for a particular flight on a particular day
• what about two passengers with the same name?
• don't we want to store some info about the passenger? Like whether he is a big fat-ass?
• now that we've paid $1 million to Oracle or IBM how much efficiency have we gained over our first naive approach?