Oracle is a Relational Database Management System. It was
designed to make it possible for allowing simultaneous access to a larger
amount of stored data. Normally RDBMS consists of the database (this contains
the physical files residing in the system and also the logical data) and the
instance. The Oracle database has two layers.
The Physical Layer – This layer consists of files like
datafiles, redo log files and control files that reside on the disk. Datafiles
consists of information contained in the database. Redo log files are used to
hold information which can be used during recovery in the event of a system
failure. Control files contain information used to start an instance.
The Logical Layer – This layer consists of one or more
tablespaces (tablespace is used to group data together logically) and the
database schema (database schema is a collection of logical structure objects)
consisting of various items such as tables, clusters, etc.
The database schema consists of:
Table – It is the basic storage unit in the Oracle database.
View – It acts as a window into one or more tables. A view, like
a table, can be updated, deleted and queried.
Cluster – It is a group of tables stored together as one table
sharing a common column.
Index – It is used to retrieve data more quickly and efficiently.
Stored Procedure – It is a predefined query that is stored in the
Sequence – It is used to generate a unique sequence of numbers in
Database Trigger – It is a procedure that is invoked
automatically when an event occurs.