oracle_db_instances1.htm
Oracle databases and instances:
  • Table spaces
  • Schemas and Users
 

On January 17, 1995 Oracle corporation released Personal Oracle, a window base version as Oracle 7 and gained immense popularity. It was operable in windows 3.1 and 95.

 Over the years the interface of Oracle Database has significantly changed. Below show Oracle DB opened with SQL Developer
An oracle database  server consists of one database and an instance (background processes and shared memory region)  of an Oracle database.

In ANSI terms, clusters contain sets of catalogs, catalog contains sets of schema, and schema contain set of object. The instance contain one or more database, databases contain one or more schemas, and schemas contain one or more tales, view or stored procedures. In windows this instance is managed by the threads within the Oracle entity.

Schema and Users:

A schema is a collection of database objects like table and indexes.  A schema and user is interchangeable representing an owner of an Oracle database