The Oracle Database allocates logical space for all data in the database in addition to the physical files. The logical units of database space allocation are data blocks, extents, segments, and tablespaces. At a physical level, the data is stored in data files on a disk. The data in the data files are stored in operating system blocks.
There are two main components in the logical database structure of the Oracle database:-
- Tablespaces: The basic storage allocation in an Oracle database is a tablespace. Each tablespace is composed of one or more physical (operating system) files. The SYSTEM tablespace is used to create each and every database. Other tablespaces are created by the Database Administrator.
- Database’s schema objects: A schema in Oracle is similar to an account or a username. Each object in the database is owned by a schema. Every Oracle database is created with two initial schemas: SYS, which is used to store the data dictionary, and SYSTEM, which often stores some data dictionary extensions as well as critical tables for other tools. Other schemas are created by the DBA. Each schema can be granted quotas in any tablespace.
