person_income

A person has income of several kinds at once — base salary, bonus, commission, self-employment, rental — and each is a separate income record because qualification treats the kinds differently. This class is the join between the person and one of them.

Making the relationship its own class is what allows the several-to-several case without a compound key: two applicants can be attributed a share of the same rental income, and one applicant can hold six income records, using the same shape in both directions.

Income writes one of these per record it returns, and the qualification layer under Income reads them to decide which figures may be counted.