vocabulary Monogamy
;
/*
* Value Types */
Name is written as String; Person ID is written as Auto Counter;
/*
* Entity Types */
Person is identified by its ID; Person is called one Name;
Boy is a kind of Person;
Girl is a kind of Person; Girl (as Girlfriend) is going out with at most one Boy (as Boyfriend) [symmetric],
Boyfriend is going out with at most one Girlfriend;
/*
* Constraints: */
either Person is a Girl or Person is a Boy but not both;