never allowed to be dropped.
   Also, knowing that pinned objects will not be dropped, the dependency
   mechanism doesn't bother to make <structname>pg_depend</structname>
   entries showing dependencies on them.  Thus, for example, a table
   column of type <type>numeric</type> notionally has
   a <literal>NORMAL</literal> dependency on the <type>numeric</type>
   data type, but no such entry actually appears
   in <structname>pg_depend</structname>.
  </para>

 </sect1>


 <sect1 id="catalog-pg-description">
  <title><structname>pg_description</structname></title>

  <indexterm zone="catalog-pg-description">
   <primary>pg_description</primary>
  </indexterm>

  <para>
   The catalog <structname>pg_description</structname> stores optional descriptions
   (comments) for each database object.  Descriptions can be manipulated
   with the <link linkend="sql-comment"><command>COMMENT</command></link> command and viewed with
   <application>psql</application>'s <literal>\d</literal> commands.
   Descriptions of many built-in system objects are provided in the initial
   contents of <structname>pg_description</structname>.
  </para>

  <para>
   See also <link linkend="catalog-pg-shdescription"><structname>pg_shdescription</structname></link>,
   which performs a similar function for descriptions involving objects that
   are shared across a database cluster.
  </para>

  <table>
   <title><structname>pg_description</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>objoid</structfield> <type>oid</type>
       (references any OID column)
      </para>
      <para>
       The OID of the object this description pertains to
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>classoid</structfield> <type>oid</type>
       (references <link linkend="catalog-pg-class"><structname>pg_class</structname></link>.<structfield>oid</structfield>)
      </para>
      <para>
       The OID of the system catalog this object appears in
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>objsubid</structfield> <type>int4</type>
      </para>
      <para>
       For a comment on a table column, this is the column number (the
       <structfield>objoid</structfield> and <structfield>classoid</structfield> refer to
       the table itself).  For all other object types, this column is
       zero.
      </para></entry>
     </row>

     <row>
      <entry role="catalog_table_entry"><para role="column_definition">
       <structfield>description</structfield> <type>text</type>
      </para>
      <para>
       Arbitrary text that serves as the description of this object
      </para></entry>
     </row>
    </tbody>
   </tgroup>
  </table>

 </sect1>


 <sect1 id="catalog-pg-enum">
  <title><structname>pg_enum</structname></title>

  <indexterm zone="catalog-pg-enum">
   <primary>pg_enum</primary>
  </indexterm>

  <para>
   The <structname>pg_enum</structname> catalog contains entries
   showing the values and labels for each enum type. The
   internal representation of a given enum value is actually the OID
   of its associated row in <structname>pg_enum</structname>.
  </para>

  <table>
   <title><structname>pg_enum</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">