One characteristic of an RDBMS is the independence of logical data structures such as tables, views
, and indexes from physical storage structures. Because physical and logical structures are separate, you can manage physical storage of data without affecting access to logical structures. For example, renaming a database file does not rename the tables stored in it.
An Oracle database is a set of files that store Oracle data in persistent disk storage. This section discusses the database files generated when you issue a CREATE DATABASE statement:
- Data files and temp files: A data file is a physical file on disk that was created by Oracle Database and contains data structures such as tables and indexes. A temp file is a data file that belongs to a temporary tablespace. The data is written to these files in an Oracle proprietary format that cannot be read by other programs.
- Control files: A control file is a root file that tracks the physical components of the database.
- Online redo log files: The online redo log is a set of files containing records of changes made to data.
A database instance is a set of memory structures that manage database files.
Figure 2-2 shows the relationship between the instance and the files that it manages.