@namespace(uri="DB", prefix="DB")
package DB;

abstract class NamedElement {
    attr String name;
}

class Database {
   val DatabaseElement[*]#database contents;
}

abstract class DatabaseElement extends NamedElement {
   ref Database#contents database;
}

class Table extends DatabaseElement {
   val Column[*]#table columns;
   ref Column[*] primaryKeys;
}

class Column extends DatabaseElement {
   ref Table#columns table;
   attr String type;
}

class ForeignKey extends DatabaseElement {
   ref Column parent;
   ref Column child;
   attr Boolean isMany;
}