</para>
      <para>
       Array of <type>regclass</type> OIDs for the extension's configuration
       table(s), or <literal>NULL</literal> if none
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>extcondition</structfield> <type>text[]</type>
      </para>
      <para>
       Array of <literal>WHERE</literal>-clause filter conditions for the
       extension's configuration table(s), or <literal>NULL</literal> if none
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

  <para>
   Note that unlike most catalogs with a <quote>namespace</quote> column,
   <structfield>extnamespace</structfield> is not meant to imply
   that the extension belongs to that schema.  Extension names are never
   schema-qualified.  Rather, <structfield>extnamespace</structfield>
   indicates the schema that contains most or all of the extension's
   objects.  If <structfield>extrelocatable</structfield> is true, then
   this schema must in fact contain all schema-qualifiable objects
   belonging to the extension.
  </para>
 </sect1>


 <sect1 id="catalog-pg-foreign-data-wrapper">
  <title><structname>pg_foreign_data_wrapper</structname></title>

  <indexterm zone="catalog-pg-foreign-data-wrapper">
   <primary>pg_foreign_data_wrapper</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_foreign_data_wrapper</structname> stores
   foreign-data wrapper definitions.  A foreign-data wrapper is the
   mechanism by which external data, residing on foreign servers, is
   accessed.
  </para>

  <table>
   <title><structname>pg_foreign_data_wrapper</structname> Columns</title>
   <tgroup cols="1">
    <thead>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       Column Type
      </para>
      <para>
       Description
      </para></entry>
     </row>
    </thead>

    <tbody>
     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>oid</structfield> <type>oid</type>
      </para>
      <para>
       Row identifier
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwname</structfield> <type>name</type>
      </para>
      <para>
       Name of the foreign-data wrapper
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwowner</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-authid"><structname>pg_authid</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       Owner of the foreign-data wrapper
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwhandler</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       References a handler function that is responsible for
       supplying execution routines for the foreign-data wrapper.
       Zero if no handler is provided
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwvalidator</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-proc"><structname>pg_proc</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       References a validator function that is responsible for
       checking the validity of the options given to the
       foreign-data wrapper, as well as options for foreign servers and user
       mappings using the foreign-data wrapper.  Zero if no validator
       is provided
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>fdwacl</structfield>