Overview of the Database System 
MaxDB is SAP’s own relational database system. You can use it in SAP solutions as a less expensive alternative to databases from other vendors.
A database instance comprises a database and the additional information required for the operation of the database. A database is a set of data with a regular structure. The data in a database is comprised of the application data (data records) and the database catalog (metadata).
Every database instance has a unique name. A database instance can be in different operational states, for example ONLINE, ADMIN, OFFLINE. In the ONLINE operational state, users can work with the data in the database instance, while the ADMIN operational state allows database administrators to execute administration tasks.
As a user, to query or change data in a database, you use the Structured Query Language (SQL). Using SQL, you can display, change and delete the logical units (database objects) of the database instance, such as tables. You can use schemas to group database objects logically. See SQL.
The database system uses transactions. See Transactions.
In physical terms, a database instance comprises the data and log volumes (permanent storage), multiple caches, the files in the run directory and a collection of metadata (including configuration files, database parameters, paths of the volumes, etc.). The database system uses page chains and B* trees as logical access structures. See Data Storage.
See also:
Creating and Configuring a Database Instance