Apps that handle lots of data will require a built-in database. e-commerce apps are one good example. This database is part of the app and data can be stored inside. This configuration is different from a database at the backend server. In a broader sense, database at the app level will handle data related to the specific user, while the server database will store data/information related to all the users.
Typically we incorporate sqlite database for app. Sqlite is a small database engine that uses SQL as the interfacing programming language. It is suitable for small applications like mobile app. Zoliotech developers use it for both IOS and Android app. Same database design can go in both platforms and this ensures data integrity to some extent across platform implementations.