Oracle Database

Oracle Database is an object-relational database management system. An application connects to a database service and uses SQL to read or change data. The database engine enforces data rules, coordinates concurrent work, and records changes so it can recover after a failure.

Start by separating the database from the instance. The database is the set of physical files that hold data, control information, and redo. An instance is the memory structures and background processes that manage those files. This distinction explains why starting an instance and opening a database are separate operations.