Oracle Database is a relational database with object and Extensible Markup Language (XML) capabilities. In a relational database, all data is stored in two-dimensional tables that are composed of rows and columns. Oracle Database enables you to store data, update it, and efficiently retrieve it, with a high degree of performance, reliability, and scalability.
Oracle Database is composed of the following elements:
The Oracle software that you install on your host computer
The database, which is a collection of physical files on one or more disks
The database contains user data, metadata, and control structures. Metadata, or data about the data, is the collection of information about a disk that permits Oracle software to manage user data. An example of metadata is the data dictionary. Control structures (such as the control file and redo log) ensure the integrity, availability, and recoverability of user data.
The Oracle instance, which is composed of the following:
The background processes, which are the operating system processes or threads that perform the work of accessing, storing, monitoring, and recovering user data, metadata, and control files associated with the database
The shared memory areas used by the background processes
Server processes that perform work on behalf of connected users and applications, and the memory and temporary storage used by these processes
Server processes parse and execute SQL statements, and retrieve and return results to the user or application.
Oracle Net, which is a software layer that enables client applications and Oracle Database to communicate over a network, and the Oracle Net listener, which is a process that listens for connection requests from the network.
Notes From OTN