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Oracle9i Database Concepts
Release 2 (9.2)

Part Number A96524-01
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This manual describes all features of the Oracle server, an object-relational database management system. It describes how the Oracle server functions and lays a conceptual foundation for much of the practical information contained in other Oracle server manuals. Information in this manual applies to the Oracle server running on all operating systems.

This preface contains these topics:


Oracle9i 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 Server"

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

Part II: Database Structures

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, "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.

Part III: The Oracle Instance

Chapter 5, "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.

Chapter 6, "Application Architecture"

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

Chapter 7, "Memory Architecture"

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

Chapter 8, "Process Architecture"

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

Chapter 9, "Database Resource Management"

This chapter describes how the Database Resource Manager can be used to control resource use.

Part IV: Data

Chapter 10, "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 11, "Partitioned Tables and Indexes"

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

Chapter 12, "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 13, "Object Datatypes and Object Views"

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

Part V: Data Access

Chapter 14, "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 procedural language constructs called procedures, functions, and packages, which are PL/SQL program units that are stored in the database.

Chapter 15, "Dependencies Among Schema Objects"

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

Chapter 16, "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 17, "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.

Part VI: Parallel SQL and Direct-Path INSERT

Chapter 18, "Parallel Execution of SQL Statements"

This chapter describes parallel execution of SQL statements (queries, DML, and DDL statements) and explains the rules for parallelizing SQL statements.

Chapter 19, "Direct-Path INSERT"

This chapter describes the Oracle direct-path INSERT feature for serial or parallel inserts, and the NOLOGGING clause.

Part VII: Data Protection

Chapter 20, "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 21, "Data Integrity"

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

Chapter 22, "Controlling Database Access"

This chapter describes how to control user access to data and database resources.

Chapter 23, "Privileges, Roles, and Security Policies"

This chapter discusses security at the system and schema object levels.

Chapter 24, "Auditing"

This chapter discusses how the Oracle auditing feature tracks database activity.

Appendix A, "Operating System Specific Information"

This appendix lists all the operating system specific references within this manual.

Appendix B, "Information on Deprecated Features"

This appendix contains conceptual information that might be of interest if you created your database with an earlier version of Oracle.


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 Oracle9i Sample Schemas for information on how these schemas were created and how you can use them yourself.

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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


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.


Italic typeface indicates book titles or emphasis.

Oracle9i 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, usernames, 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, usernames 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 

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 
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 
sqlplus hr/hr

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 Corporation 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.

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