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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>36.1. How Extensibility Works</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="extend.html" title="Chapter 36. Extending SQL" /><link rel="next" href="extend-type-system.html" title="36.2. The PostgreSQL Type System" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">36.1. How Extensibility Works</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="extend.html" title="Chapter 36. Extending SQL">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="extend.html" title="Chapter 36. Extending SQL">Up</a></td><th width="60%" align="center">Chapter 36. Extending <acronym class="acronym">SQL</acronym></th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 18.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="extend-type-system.html" title="36.2. The PostgreSQL Type System">Next</a></td></tr></table><hr /></div><div class="sect1" id="EXTEND-HOW"><div class="titlepage"><div><div><h2 class="title" style="clear: both">36.1. How Extensibility Works <a href="#EXTEND-HOW" class="id_link">#</a></h2></div></div></div><p>
    <span class="productname">PostgreSQL</span> is extensible because its operation  is
    catalog-driven.   If  you  are familiar with standard
    relational database systems, you know that  they  store  information
    about  databases,  tables,  columns,  etc., in what are
    commonly known as system catalogs.  (Some systems  call
    this  the data dictionary.)  The catalogs appear to the
    user as tables like any other, but  the  <acronym class="acronym">DBMS</acronym>  stores
    its  internal  bookkeeping in them.  One key difference
    between <span class="productname">PostgreSQL</span> and  standard  relational database systems  is
    that <span class="productname">PostgreSQL</span> stores much more information in its
    catalogs: not only information about tables and  columns,
    but also information about data types, functions, access
    methods, and so on.  These tables can be  modified  by
    the  user, and since <span class="productname">PostgreSQL</span> bases its operation
    on these tables, this means that <span class="productname">PostgreSQL</span> can  be
    extended   by   users.    By  comparison,  conventional
    database systems can only be extended by changing hardcoded
    procedures in the source code or by loading modules
    specially written by the <acronym class="acronym">DBMS</acronym> vendor.
   </p><p>
    The <span class="productname">PostgreSQL</span> server can moreover
    incorporate user-written code into itself through dynamic loading.
    That is, the user can specify an object code file (e.g., a shared
    library) that implements a new type or function, and
    <span class="productname">PostgreSQL</span> will load it as required.
    Code written in <acronym class="acronym">SQL</acronym> is even more trivial to add
    to the server.  This ability to modify its operation <span class="quote">“<span class="quote">on the
    fly</span>”</span> makes <span class="productname">PostgreSQL</span> uniquely
    suited for rapid prototyping of new applications and storage
    structures.
   </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="extend.html" title="Chapter 36. Extending SQL">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extend.html" title="Chapter 36. Extending SQL">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="extend-type-system.html" title="36.2. The PostgreSQL Type System">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 36. Extending <acronym class="acronym">SQL</acronym> </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 18.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 36.2. The <span class="productname">PostgreSQL</span> Type System</td></tr></table></div></body></html>