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Oracle® Database Concepts
10g Release 1 (10.1)

Part Number B10743-01
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This manual describes all features of the Oracle database server, an object-relational database management system. It describes how the Oracle database server functions, and it lays a conceptual foundation for much of the practical information contained in other manuals. Information in this manual applies to the Oracle database server running on all operating systems.

This preface contains these topics:


Oracle Database Concepts is intended for database administrators, system administrators, and database application developers.

To use this document, you need to know the following:


This document contains:

Part I, "What Is Oracle?"

Chapter 1, " Introduction to the Oracle Database"

This chapter provides an overview of the concepts and features you need for understanding the Oracle database server. You should read this overview before using the detailed information in the remainder of this manual.

Part II, "Oracle Database Architecture"

Chapter 2, " Data Blocks, Extents, and Segments"

This chapter discusses how data is stored and how storage space is allocated for and consumed by various objects within an Oracle database.

Chapter 3, " Tablespaces, Datafiles, and Control Files"

This chapter discusses how physical storage space in an Oracle database is divided into logical divisions called tablespaces. It also discusses the physical operating system files associated with tablespaces (datafiles) and files used in recovery (control files).

Chapter 4, " Transaction Management "

This chapter defines the concept of transactions and explains the SQL statements used to control them. Transactions are logical units of work that are run together as a unit.

Chapter 5, " Schema Objects "

This chapter describes the database objects that can be created in the domain of a specific user (a schema), including tables, views, numeric sequences, and synonyms. Optional structures that make data retrieval more efficient, including indexes, materialized views, dimensions, and clusters, are also described.

Chapter 6, " Dependencies Among Schema Objects "

This chapter explains how Oracle manages the dependencies for objects such as procedures, packages, triggers, and views.

Chapter 7, " The Data Dictionary"

This chapter describes the data dictionary, which is a set of reference tables and views that contain read-only information about an Oracle database.

Chapter 8, " Memory Architecture"

This chapter describes the memory structures used by an Oracle database system.

Chapter 9, " Process Architecture "

This chapter describes the process architecture of an Oracle instance and the different process configurations available for Oracle.

Chapter 10, " Application Architecture"

This chapter discusses distributed processing environments in which the Oracle database server can operate.

Chapter 11, " Oracle Utilities"

This chapter describes Oracle database utilities for data transfer, data maintenance, and database administration. These include Data Pump Export/Import, SQL*Loader, and LogMiner.

Chapter 12, " Database and Instance Startup and Shutdown"

This chapter describes an Oracle instance and explains how the database administrator can control the accessibility of an Oracle database system.

Part III, "Oracle Database Features"

Chapter 13, " Data Concurrency and Consistency "

This chapter explains how Oracle provides concurrent access to and maintains the accuracy of shared information in a multiuser environment. It describes the automatic mechanisms that Oracle uses to guarantee that the concurrent operations of multiple users do not interfere with each other.

Chapter 14, " Manageability"

This chapter describes features for managing database use, such as Oracle Enterprise Manager, Automatic Storage Management, the Database Resource Manager, and the Scheduler.

Chapter 15, " Backup and Recovery"

This chapter introduces database concepts that are fundamental to backing up a database. It also introduces the structures that are used during database recovery.

Chapter 17, " High Availability"

This chapter provides an overview of Oracle's high available features, including data protection, online reorganization and redfinition of tables and indexes, dynamic resizing of memory structures, and database repair.

Chapter 16, " Business Intelligence"

This chapter describes Oracle's business intelligence features, including data warehousing, parallel execution, data mining, and OLAP functions.

Chapter 18, " Partitioned Tables and Indexes"

This chapter describes how partitioning can be used to split large tables and indexes into more manageable pieces.

Chapter 19, " Content Management"

This chapter provides an overview of Oracle's content management features, including XML, Oracle Text, Oracle Ultra Search, and Oracle Spatial.

Chapter 20, " Database Security "

This chapter describes how to control user access to data and database resources. It also discusses security at the system and schema object levels, and it explains how Oracle auditing tracks database activity.

Chapter 21, " Data Integrity"

This chapter discusses data integrity and the declarative integrity constraints that you can use to enforce data integrity.

Chapter 22, " Triggers "

This chapter discusses triggers, which are procedures written in PL/SQL, Java, or C that run implicitly whenever a table or view is modified or when some user actions or database system actions occur.

Chapter 23, " Information Integration"

This chapter explains Oracle's various solutions for operating in a distributed environment, including Oracle Streams and Distributed SQL.

Part IV, "Oracle Database Application Development"

Chapter 24, " SQL, PL/SQL, and Java"

This chapter briefly describes SQL (Structured Query Language), the language used to communicate with Oracle, as well as PL/SQL, the Oracle procedural language extension to SQL. It also discusses the procedures, functions, and packages, which are PL/SQL program units stored in the database.

Chapter 25, " Overview of Application Development Languages"

This chapter describes Oracle APIs for accessing various information.

Chapter 26, " Native Datatypes "

This chapter describes the types of relational data that can be stored in an Oracle database table, such as fixed- and variable-length character strings, numbers, dates, and binary large objects (BLOBs).

Chapter 27, " Object Datatypes and Object Views"

This chapter gives an overview of the object extensions that Oracle provides.


The glossary defines terms used in this manual.

Related Documentation

For more information, see these Oracle resources:

Many books in the documentation set use the sample schemas of the seed database, which is installed by default when you install Oracle. Refer to Oracle Database Sample Schemas for information on how these schemas were created and how you can use them yourself.

Printed documentation is available for sale in the Oracle Store at

To download free release notes, installation documentation, white papers, or other collateral, please visit the Oracle Technology Network (OTN). You must register online before using OTN; registration is free and can be done at

If you already have a username and password for OTN, then you can go directly to the documentation section of the OTN Web site at


This section describes the conventions used in the text and code examples of this documentation set. It describes:

Conventions in Text

We use various conventions in text to help you more quickly identify special terms. The following table describes those conventions and provides examples of their use.

Convention Meaning Example
Boldtbl Bold typeface indicates terms that are defined in the text or terms that appear in a glossary, or both. When you specify this clause, you create an index-organized table.
Italics Italic typeface indicates book titles or emphasis. Oracle Database Concepts

Ensure that the recovery catalog and target database do not reside on the same disk.

UPPERCASE monospace (fixed-width) font Uppercase monospace typeface indicates elements supplied by the system. Such elements include parameters, privileges, datatypes, RMAN keywords, SQL keywords, SQL*Plus or utility commands, packages and methods, as well as system-supplied column names, database objects and structures, user names, and roles. You can specify this clause only for a NUMBER column.

You can back up the database by using the BACKUP command.

Query the TABLE_NAME column in the USER_TABLES data dictionary view.


lowercase monospace (fixed-width) font Lowercase monospace typeface indicates executables, filenames, directory names, and sample user-supplied elements. Such elements include computer and database names, net service names, and connect identifiers, as well as user-supplied database objects and structures, column names, packages and classes, user names and roles, program units, and parameter values.

Note: Some programmatic elements use a mixture of UPPERCASE and lowercase. Enter these elements as shown.

Enter sqlplus to open SQL*Plus.

The password is specified in the orapwd file.

Back up the datafiles and control files in the /disk1/oracle/dbs directory.

The department_id, department_name, and location_id columns are in the hr.departments table.

Set the QUERY_REWRITE_ENABLED initialization parameter to true.

Connect as oe user.

The JRepUtil class implements these methods.

lowercase italic monospace (fixed-width) font Lowercase italic monospace font represents placeholders or variables. You can specify the parallel_clause.

Run Uold_release.SQL where old_release refers to the release you installed prior to upgrading.

Conventions in Code Examples

Code examples illustrate SQL, PL/SQL, SQL*Plus, or other command-line statements. They are displayed in a monospace (fixed-width) font and separated from normal text as shown in this example:

SELECT username FROM dba_users WHERE username = 'MIGRATE';

The following table describes typographic conventions used in code examples and provides examples of their use.

Convention Meaning Example
[ ]
Brackets enclose one or more optional items. Do not enter the brackets.
DECIMAL (digits [ , precision ])
{ }
Braces enclose two or more items, one of which is required. Do not enter the braces.

A vertical bar represents a choice of two or more options within brackets or braces. Enter one of the options. Do not enter the vertical bar.
Horizontal ellipsis points indicate either:
  • That we have omitted parts of the code that are not directly related to the example

  • That you can repeat a portion of the code

CREATE TABLE ... AS subquery;

SELECT col1, col2, ... , coln FROM employees;
Vertical ellipsis points indicate that we have omitted several lines of code not directly related to the example.
9 rows selected.
Other notation You must enter symbols other than brackets, braces, vertical bars, and ellipsis points as shown.
acctbal NUMBER(11,2);
acct    CONSTANT NUMBER(4) := 3;
Italicized text indicates placeholders or variables for which you must supply particular values.
CONNECT SYSTEM/system_password
DB_NAME = database_name
Uppercase typeface indicates elements supplied by the system. We show these terms in uppercase in order to distinguish them from terms you define. Unless terms appear in brackets, enter them in the order and with the spelling shown. However, because these terms are not case sensitive, you can enter them in lowercase.
SELECT last_name, employee_id FROM employees;
DROP TABLE hr.employees;
Lowercase typeface indicates programmatic elements that you supply. For example, lowercase indicates names of tables, columns, or files.

Note: Some programmatic elements use a mixture of UPPERCASE and lowercase. Enter these elements as shown.

SELECT last_name, employee_id FROM employees;
sqlplus hr/hr

Conventions for Windows Operating Systems

The following table describes conventions for Windows operating systems and provides examples of their use.

Convention Meaning Example
Choose Start > How to start a program. To start the Database Configuration Assistant, choose Start > Programs > Oracle - HOME_NAME > Configuration and Migration Tools > Database Configuration Assistant.
File and directory names File and directory names are not case sensitive. The following special characters are not allowed: left angle bracket (<), right angle bracket (>), colon (:), double quotation marks ("), slash (/), pipe (|), and dash (-). The special character backslash (\) is treated as an element separator, even when it appears in quotes. If the file name begins with \\, then Windows assumes it uses the Universal Naming Convention.
c:\winnt"\"system32 is the same as C:\WINNT\SYSTEM32
C:\> Represents the Windows command prompt of the current hard disk drive. The escape character in a command prompt is the caret (^). Your prompt reflects the subdirectory in which you are working. Referred to as the command prompt in this manual.
Special characters The backslash (\) special character is sometimes required as an escape character for the double quotation mark (") special character at the Windows command prompt. Parentheses and the single quotation mark (') do not require an escape character. Refer to your Windows operating system documentation for more information on escape and special characters.
C:\>exp scott/tiger TABLES=emp QUERY=\"WHERE job='SALESMAN' and sal<1600\"
C:\>imp SYSTEM/password FROMUSER=scott TABLES=(emp, dept)
Represents the Oracle home name. The home name can be up to 16 alphanumeric characters. The only special character allowed in the home name is the underscore.
C:\> net start OracleHOME_NAMETNSListener
ORACLE_HOME and ORACLE_BASE In releases prior to Oracle8i release 8.1.3, when you installed Oracle components, all subdirectories were located under a top level ORACLE_HOME directory that by default used one of the following names:
  • C:\orant for Windows NT

  • C:\orawin98 for Windows 98

This release complies with Optimal Flexible Architecture (OFA) guidelines. All subdirectories are not under a top level ORACLE_HOME directory. There is a top level directory called ORACLE_BASE that by default is C:\oracle. If you install the latest Oracle release on a computer with no other Oracle software installed, then the default setting for the first Oracle home directory is C:\oracle\orann, where nn is the latest release number. The Oracle home directory is located directly under ORACLE_BASE.

All directory path examples in this guide follow OFA conventions.

Refer to Oracle Database Platform Guide for Windows for additional information about OFA compliances and for information about installing Oracle products in non-OFA compliant directories.

Go to the ORACLE_BASE\ORACLE_HOME\rdbms\admin directory.

Documentation Accessibility

Our goal is to make Oracle products, services, and supporting documentation accessible, with good usability, to the disabled community. To that end, our documentation includes features that make information available to users of assistive technology. This documentation is available in HTML format, and contains markup to facilitate access by the disabled community. Standards will continue to evolve over time, and Oracle is actively engaged with other market-leading technology vendors to address technical obstacles so that our documentation can be accessible to all of our customers. For additional information, visit the Oracle Accessibility Program Web site at

Accessibility of Code Examples in Documentation

JAWS, a Windows screen reader, may not always correctly read the code examples in this document. The conventions for writing code require that closing braces should appear on an otherwise empty line; however, JAWS may not always read a line of text that consists solely of a bracket or brace.

Accessibility of Links to External Web Sites in Documentation

This documentation may contain links to Web sites of other companies or organizations that Oracle does not own or control. Oracle neither evaluates nor makes any representations regarding the accessibility of these Web sites.