Link with & in it

Hello,

how can I put into a docbook document a link with contains the special sign "&"? I tried <![CDATA[&]]> but then the Xinclude does not work anymore.

[Fatal Error] counter_feedback.xml:13:48: The value of attribute "url" associated with an element type "ulink" must not contain the '<' character.

For example the text would look like:

<para>
                Alternatively you can provide feedback to this article in this
                guestbook
                <ulink
                        url="http://www.url.de/tinc?key=y7sfdsfS&start=-1&reverse=1">
                        Link for guestbook
                </ulink>

</para>

Best regards, Lars