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Oracle Essentials: Oracle9i, Oracle8i and Oracle8, Second Edition by Jonathan Stern, Robert Stackowiak, Rick Greenwald

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The Components of a Database

When you create a database, you assign a specific name to it. You cannot change the database name once you have created it, although you can change the name of the instance that accesses the database.

This section covers the different types of files and other components that make up a complete database.

Tablespaces

Before you examine the physical files of the actual database, you need to understand a key logical structure within a database, the tablespace. All the data stored in a database must reside in a tablespace.

A tablespace is a logical structure; you cannot look at the operating system and see a tablespace. Each tablespace is composed of physical structures called datafiles; each tablespace must consist of one or more datafiles, and each datafile can belong to only one tablespace. When you create a table, you can specify which tablespace in which to create it. Oracle will then find space for it in one of the datafiles that make up the tablespace.

Figure 2-2 shows the relationship of tablespaces to datafiles for a database.

Tablespaces and datafiles

Figure 2-2. Tablespaces and datafiles

This figure shows two tablespaces within an Oracle database. When you create a new table in this Oracle database, you may place it in the DATA1 tablespace or the DATA2 tablespace. It will physically reside in one of the datafiles that make up the specified tablespace.

Physical Files in an ...

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