No doubt you spent a lot of time planning your database, mapping out its structure, before you created it. Even the most thorough planners, however, may discover that their databases require a few changes. For example, you may find that you need to add new fields or remove existing ones. You can also make changes to your database to make data entry easier, such as setting default values in fields. You can even make changes to your database to ensure that entries are valid, such as requiring a unique entry in an ID field. That's the focus of this part: making changes to enhance your database's usability.