The synchronisation makes the tables in the database match the tables of the model. It compares the tables, columns, indexes and referential constraints of the repository with the database and creates, adds or changes what differs. A column added to a table that already holds rows can get a value for those rows from its "Conversion" expression, such as `coalesce(:orig, sysdate)`. Without a conversion the new column starts empty. The synchronisation runs before the [[Invantive Studio/Repository/Concepts/Generation of the Business Layer|generation of the business layer]], because the business layer is built on the tables.