Database Manager

1. The database manager is a program module which provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system.

2. Databases typically require lots of storage space (gigabytes). This must be stored on disks. Data is moved between disk and main memory (MM) as needed.

3. The goal of the database system is to simplify and facilitate access to data. Performance is important. Views provide simplification.

4. So the database manager module is responsible for
   • Interaction with the file manager: Storing raw data on disk using the file system usually provided by a conventional operating system. The database manager must translate DML statements into low-level file system commands (for storing, retrieving and updating data in the database).

   • Integrity enforcement: Checking that updates in the database do not violate consistency constraints (e.g. no bank account balance below $25)

   • Security enforcement: Ensuring that users only have access to information they are permitted to see

   • Backup and recovery: Detecting failures due to power failure, disk crash, software errors, etc., and restoring the database to its state before the failure

   • Concurrency control: Preserving data consistency when there are concurrent users.
5. Some small database systems may miss some of these features, resulting in simpler database managers. (For example, no concurrency is required on a PC running MS-DOS.) These features are necessary on larger systems.