![]() Field travel_id of DB table for Booking entity has a foreign key relationship to field travel_id of DB table for travel entity.This means, travel is the parent entity and bookings are child entities.Any new booking(instance) created for entity booking should belong to entity set travel.DB table for Booking entity has booking_id and travel_id as primary keys.Any new travel(instance) created for travel entity will be identified with this primary key.DB table for Travel entity has travel_id as primary key.In this scenario, primary keys-travel_id, booking_id and booking_supplement_id are sematic keys. ![]() Create database tables for data persistence and create parent-child relationship via foreign key associations.Perform calculations, validate input values and reject instance creation (if needed).Possibility to create, update and delete any node-no orphans allowed.A booking supplement cannot exist without a booking-– no orphans allowed.A booking cannot exist without a valid travel – no orphans allowed.A travel can exist without a valid booking – only root as single node is allowed.Booking supplement is grandchild node of travel. ![]()
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