preferred over version 3 because SHA-1 is thought to be more secure
        than MD5.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
  </table>

  <table id="uuid-ossp-constants">
   <title>Functions Returning UUID Constants</title>
    <tgroup cols="1">
     <thead>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        Function
       </para>
       <para>
        Description
       </para></entry>
      </row>
     </thead>

     <tbody>
      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>uuid_nil</function> ()
        <returnvalue>uuid</returnvalue>
       </para>
       <para>
        Returns a <quote>nil</quote> UUID constant, which does not occur as a
        real UUID.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>uuid_ns_dns</function> ()
        <returnvalue>uuid</returnvalue>
       </para>
       <para>
        Returns a constant designating the DNS namespace for UUIDs.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>uuid_ns_url</function> ()
        <returnvalue>uuid</returnvalue>
       </para>
       <para>
        Returns a constant designating the URL namespace for UUIDs.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>uuid_ns_oid</function> ()
        <returnvalue>uuid</returnvalue>
       </para>
       <para>
        Returns a constant designating the ISO object identifier (OID) namespace for
        UUIDs.  (This pertains to ASN.1 OIDs, which are unrelated to the OIDs
        used in <productname>PostgreSQL</productname>.)
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>uuid_ns_x500</function> ()
        <returnvalue>uuid</returnvalue>
       </para>
       <para>
        Returns a constant designating the X.500 distinguished name (DN)
        namespace for UUIDs.
       </para></entry>
      </row>
     </tbody>
    </tgroup>
  </table>
 </sect2>

 <sect2 id="uuid-ossp-building">
  <title>Building <filename>uuid-ossp</filename></title>

  <para>
   Historically this module depended on the OSSP UUID library, which accounts
   for the module's name.  While the OSSP UUID library can still be found
   at <ulink url="http://www.ossp.org/pkg/lib/uuid/"></ulink>, it is not well
   maintained, and is becoming increasingly difficult to port to newer
   platforms.  <filename>uuid-ossp</filename> can now be built without the OSSP
   library on some platforms.  On FreeBSD and some other BSD-derived
   platforms, suitable UUID creation functions are included in the
   core <filename>libc</filename> library.  On Linux, macOS, and some other
   platforms, suitable functions are provided in the <filename>libuuid</filename>
   library, which originally came from the <literal>e2fsprogs</literal> project
   (though on modern Linux it is considered part
   of <literal>util-linux-ng</literal>).  When invoking <filename>configure</filename>,
   specify <option>--with-uuid=bsd</option> to use the BSD functions,
   or <option>--with-uuid=e2fs</option> to
   use <literal>e2fsprogs</literal>' <filename>libuuid</filename>, or
   <option>--with-uuid=ossp</option> to use the OSSP UUID library.
   More than one of these libraries might be available on a particular
   machine, so <filename>configure</filename> does not automatically choose one.
  </para>
 </sect2>

 <sect2 id="uuid-ossp-author">
  <title>Author</title>

  <para>
   Peter Eisentraut <email>peter_e@gmx.net</email>
  </para>

 </sect2>

</sect1>