It hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints. The external level describes how users view the data of the database. Structures and the data contained within them can be manipulated by operations. The operations on a database must comply to a predefined set of integrity rules. Integrity rules protect the data and the structures of a database.
Object types specify the structure of the data and the methods of operating on the data.
Every object type has a constructor method that makes a new object according to the data-type's specification. The advantage of this division is the distribution of processes over multiple processors. This reduces the processing load and improves the system as a whole. The server portion receives and processes the SQL statements that originate from client applications. SQL statements execute all operations on the information in an Oracle database.