DP4 derives the structure of your database from an analysis of the tables on your database. A parent-child link is derived where you include the primary key of the parent table in the child table.
For example, customers place orders, and there is a requirement to find the order record for a customer. You create a link by including the key of the CUSTOMER table, CUSTOMER_NUMBER, as a secondary key in the ORDER_HEADER table:
The database manager uses this structural information for indexing and referential integrity, and QA Build and Report Writer use it to provide predetermined access paths between records.