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 <chapter id="intro">
  <title>Introduction</title>

  <para>
   This document is the user  manual  for  the  
   <ulink url="http://postgresql.org/"><productname>PostgreSQL</productname></ulink>
   database  management system, originally developed at the University
   of California at  Berkeley.   

   <productname>PostgreSQL</productname>  is  based  on
   <ulink url="http://s2k-ftp.CS.Berkeley.EDU:8000/postgres/postgres.html">
    <productname>Postgres release 4.2</productname></ulink>. 
   The <productname>Postgres</productname> project, 
   led by Professor Michael Stonebraker, was sponsored  by  the
   Defense  Advanced Research Projects Agency
   (<acronym>DARPA</acronym>), the
   Army Research Office (<acronym>ARO</acronym>), the National Science  
   Foundation (<acronym>NSF</acronym>), and ESL, Inc.
  </para>

  <sect1>
   <title> What is <productname>Postgres</productname>?</title>

   <para>
    Traditional   relational  database  management  systems
    (DBMSs) support a data model consisting of a collection
    of named relations, containing attributes of a specific
    type.  In current commercial  systems,  possible  types
    include  floating  point  numbers,  integers, character
    strings, money, and dates.  It is  commonly  recognized
    that  this model is inadequate for future data 
    processing applications.
    The relational  model  successfully  replaced  previous
    models  in  part  because  of its "Spartan simplicity".
    However, as mentioned, this simplicity often makes  the
    implementation  of  certain applications very difficult.
    <productname>Postgres</productname> offers  substantial additional
    power  by  incorporating  the following four additional
    basic concepts in such a way that  users  can  easily
    extend the system:

    <simplelist>
     <member>classes</member>
     <member>inheritance</member>
     <member>types</member>
     <member>functions</member>
    </simplelist>
   </para>

   <para>
    Other features provide additional power and flexibility:

    <simplelist>
     <member>constraints</member>
     <member>triggers</member>
     <member>rules</member>
     <member>transaction integrity</member>
    </simplelist>
   </para>

   <para>
    These features put <productname>Postgres</productname> into the
    category of databases referred to as
    <firstterm>object-relational</firstterm>. Note that this is distinct
    from those referred to as <firstterm>object-oriented</firstterm>,
    which in general are not as well suited to supporting the
    traditional relational database languages.
    So, although <productname>Postgres</productname> has some
    object-oriented features, it is firmly in the relational database
    world. In fact, some commercial databases have recently
    incorporated features pioneered by <productname>Postgres</productname>.
   </para>

  </sect1>

   &history;
   &about;
   &info;
   &notation;
   &problems;
   &y2k;
   &legal;

 </chapter>

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