You might have more than one table in the database. For example, you could have a table of current owners for quick lookup and a table of all owners for full hi

You might have more than one table in the database. For example, you could have a table of current owners for quick lookup and a table of all owners for full history. For the current owners table, you'd use just the domain as a key. For all the full history table, you'd use domain + start date + end date as the key. So yeah, that makes it a weird example, but the point is that in neither table did you make up a synthetic key. In one table, you used a real-world fact (domain) as the key, and in the other table you used three real-world facts (domain plus two dates) together as a key.