A relation from one table to another is recorded as a referential constraint: - Make sure the referring table has a column named after the alias of the other table followed by `_id`, such as `ord_id` in a table of order lines referring to orders. - Open the referring table in the tree and select its folder "Referential Constraints". - Choose [[Invantive Studio/Ribbon/Add|"Add"]] and choose the column of the referring table and the column `id` of the referred table. - Enter the role labels, which name the relation as seen from each side. - Choose [[Invantive Studio/Ribbon/Save|"Save"]]. [[Invantive Studio/Repository/Commands/Auto Complete|Auto Complete]] adds such constraints, and an index on each referring column, for every column named after another alias. A relation also tells the business objects which tables to join.