A string data type suffices for a name, an algebraic data type for the recorded sex, and a triple of integers for a date. Use a constructor for Person so that selectors are unambiguous in Haskell:
type Name = String
data Sex = Female | Male deriving (Eq, Show)
data Date = Date { day :: Int, month :: Int, year :: Int }
  deriving (Eq, Show)
data Person = Person { name :: Name, sex :: Sex, born :: Date }
  deriving (Eq, Show)
type BirthCertificate = (Person, Person, Person)
type Database = [BirthCertificate]
Dates have the precondition that their fields form a valid calendar date. This simple database representation assumes the triple of identifying fields distinguishes the recorded individuals; a production database would normally add a stable identifier to distinguish namesakes. The two constructors for Sex model the two recorded values used by this exercise. In mathematical notation,
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