Introduction:
An Oracle server is a relational database management system (RDBMS), which is
a server that manages relational data in a database.
An RDBMS (or a database server) is able to:
1. Manage large amounts of data in a multiuser environment so that many users
can concurrently access the same data
2. Maintain relationships between data
3. Control access to data in terms of security, using its own user authorization
concept
4. Recover data to point of known consistency in the event of a system failure
5. Deliver high performance for processing of data requests

In an SAP system, the only interactive user connecting to the database server
should be the database administrator. Application data processing is almost
exclusively initiated by work processes of SAP instances in the role of database
clients.

Terminology :
1. Database,
An Oracle database is a collection of data, logically treated as a unit.
Physically, the data is stored in one or more data files on disks.
Oracle manages database data in logical units called tablespaces. A database
object, such as a table, is always created in a particular tablespace. A
tablespace consists of one or more data files.
2. Instance,
The combination of Oracle (background) processes and memory
buffers.
3. SGA (System Global Area)
- a shared memory region Which allocated when every time an Oracle instance started.
- SGA can only be accessed by the processes of this instance.
- SGA contain copies of data and control information for the corresponding Oracle instance.
4. Processes
Every time an Oracle instance is started, Oracle background processes are
started. When an instance shuts down, the processes are stopped.
5. system identifier (DBSID)
- Every database is uniquely identified in the network by its system identifier.
- On SAP systems, the system identifier must consist of exactly three
characters, the first of which must be an uppercase letter, while the other two
can be uppercase letters or digits.

Database Architecture
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