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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>37.1. 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 V1.79.1" /><link rel="prev" href="extend.html" title="Chapter 37. Extending SQL" /><link rel="next" href="extend-type-system.html" title="37.2. The PostgreSQL Type System" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">37.1. How Extensibility Works</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="extend.html" title="Chapter 37. Extending SQL">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="extend.html" title="Chapter 37. Extending SQL">Up</a></td><th width="60%" align="center">Chapter 37. Extending <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym></th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="extend-type-system.html" title="37.2. The PostgreSQL Type System">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="EXTEND-HOW"><div class="titlepage"><div><div><h2 class="title" style="clear: both">37.1. How Extensibility Works</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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extend.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="extend-type-system.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 37. Extending <acronym class="acronym">SQL</acronym> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 37.2. The <span class="productname">PostgreSQL</span> Type System</td></tr></table></div></body></html>
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