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| Purpose |
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Oracle terminology of architecture and database storage are different then most other RDBMS products. This bulletin describes the architectual differences between how other RDBMS systems are organized compared to Oracle. This includes the organization of the processes, database and physical devices.
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| Scope & Application |
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Organization of databases, processes and devices in an Oracle Instance.
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| The Oracle Database Architecture. What is an Oracle Database? |
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In most RDBMS products, you have a single server that serves multiple databases. The server maintains a central database used to identify global resources.
Oracle uses the CODASYL definition of a database as a collection of schemas. Each schema equates to a SQL Server / Sybase / Informix or DB2 database. Oracle has a central schema - SYS. An Oracle instance - the database along with a number of processes - equates to a Microsoft SQL Server / Sybase server. Most RDBMS products refer to the database engines as a server or SQL Server. Oracle refers the the database engine as the Oracle Instance or Oracle Database.
The Oracle Migration Workbench creates a single schema from multiple databases and equates databases to tablespaces.
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| Other RDBMS Server | Oracle Database/Instance |
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Memory
(all RDBMS processes in same memory space)
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Master Database
Database 1
Database 2
Database 3
etc...
| Memory + a number of Oracle processes
(USER, DBWR, SMON, PMON, LGWR ...)
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System Tablespace
Tablespace 1
Tablespace 2
Tablespace 3
etc...
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