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<preface id="preface">
 <title>Preface</title>

 <para>
  This book is the official documentation of PostgreSQL.  It is being
  written by the PostgreSQL developers and other volunteers in
  parallel to the development of the PostgreSQL software.  It
  describes all the functionality that the current version of
  PostgreSQL officially supports.
 </para>

 <para>
  To make the large amount of information about PostgreSQL manageable,
  this book has been organized in several parts.  Each part is
  targeted at a different class of users, or at users in different
  stages of their PostgreSQL experience:

  <itemizedlist>
   <listitem>
    <para>
     <xref linkend="tutorial"> is an informal introduction for new users.
    </para>
   </listitem>

   <listitem>
    <para>
     <xref linkend="sql"> documents the <acronym>SQL</acronym> query
     language environment, including data types and functions, as well
     as user-level performance tuning.  Every
     <productname>PostgreSQL</> user should read this.
    </para>
   </listitem>

   <listitem>
    <para>
     <xref linkend="admin"> describes the installation and
     administration of the server.  Everyone that runs a PostgreSQL
     server, be it for private use or for others, should read this
     part.
    </para>
   </listitem>

   <listitem>
    <para>
     <xref linkend="client-interfaces"> describes the programming
     interfaces for PostgreSQL client programs.
    </para>
   </listitem>


   <listitem>
    <para>
     <xref linkend="server-programming"> contains information for
     advanced users about the extensibility capabilities of the
     server.  Topics are, for instance, user-defined data types and
     functions.
    </para>
   </listitem>

   <listitem>
    <para>
     <xref linkend="reference"> contains information about the syntax
     of SQL commands, client and server programs.  This part supports
     the other parts with structured information sorted by command or
     program.
    </para>
   </listitem>
  </itemizedlist>
 </para>

 <sect1 id="intro-whatis">
  <title> What is <productname>PostgreSQL</productname>?</title>

  <para>
   <productname>PostgreSQL</productname> is an object-relational
   database management system (<acronym>ORDBMS</acronym>) based on
   <ulink url="http://s2k-ftp.CS.Berkeley.EDU:8000/postgres/postgres.html">
   <productname>POSTGRES, Version 4.2</productname></ulink>, developed
   at the University of California at Berkeley Computer Science
   Department.  POSTGRES pioneered many concepts that only became
   available in some commercial database systems much later.
  </para>

  <para>
   <productname>PostgreSQL</productname> is an open-source descendant
   of this original Berkeley code.  It supports SQL92 and SQL99 and
   offers many modern features:

   <itemizedlist spacing="compact">
    <listitem>
     <simpara>complex queries</simpara>
    </listitem>
    <listitem>
     <simpara>foreign keys</simpara>
    </listitem>
    <listitem>
     <simpara>triggers</simpara>
    </listitem>
    <listitem>
     <simpara>views</simpara>
    </listitem>
    <listitem>
     <simpara>transactional integrity</simpara>
    </listitem>
    <listitem>
     <simpara>multiversion concurrency control</simpara>
    </listitem>
   </itemizedlist>

   Also, PostgreSQL can be extended by the user in many ways, for
   example by adding new

   <itemizedlist spacing="compact">
    <listitem>
     <simpara>data types</simpara>
    </listitem>
    <listitem>
     <simpara>functions</simpara>
    </listitem>
    <listitem>
     <simpara>operators</simpara>
    </listitem>
    <listitem>
     <simpara>aggregate functions</simpara>
    </listitem>
    <listitem>
     <simpara>index methods</simpara>
    </listitem>
    <listitem>
     <simpara>procedural languages</simpara>
    </listitem>
   </itemizedlist>
  </para>

  <para>
   And because of the liberal license, PostgreSQL can be used,
   modified, and distributed by everyone free of charge for any
   purpose, be it private, commercial, or academic.
  </para>
 </sect1>

 &history;
 &notation;
 &info;
 &problems;

</preface>
