An external identifier (also called XML ID) is a human-readable string identifier that uniquely identifies a particular record in Odoo. They are important when loading data into Odoo.

One reason for that is when upgrading a module, its data files will be loaded again into the database, and we need to detect the already existing records, in order to update them instead of creating new duplicate records.

Another reason supporting interrelated data: data records must be able to reference other data records. The actual database identifier is a sequential number automatically assigned by the database, during module installation. The external identifiers provides a way to reference a related record without the need to know beforehand what database ID it will be assigned, allowing us to define data relations in Odoo data files.

Odoo takes care of translating the external identifier names into actual database IDs assigned to them. The mechanism behind this is quite...