A Control file records the physical structure of the database. It contains the following information.
Database Name, Names and locations of a databases files and redolog files. ,Time stamp of database creation.
When an instance of an ORACLE database is started, its control file is used to identify the database and redo log files that must be opened for database operation to proceed. It is also used in database recovery.
The data dictionary of an ORACLE database is a set of tables and views that are used as a read-only reference about the database. It stores information about both the logical and physical structure of the database, the valid users of an ORACLE database, integrity constraints defined for tables in the database and space allocated for a schema object and how much of it is being used.
An integrity constraint is a declarative way to define a business rule for a column of a table.
SGA and ORACLE background processes constitute an ORACLE instance. (or) Combination of memory structure and background process.