help with xpath namespace

I am trying to use xpath to extract some information from a XML document.
(if it matters, It's the router config for a Juniper router)

I believe I am having problems with the namespace.
I am trying to extract the serial-number, but I am not getting anything.

Here is the script I have been testing with:


BEGIN;

CREATE TABLE "xml_test" (       data_xml        xml
);


INSERT INTO xml_test (data_xml) VALUES ('<chassis-inventory xmlns="http://xml.juniper.net/junos/9.6R4/junos-chassis">
<chassisjunos:style="inventory">    <name>Chassis</name>    <serial-number>JN1111111111</serial-number>
<description>MX960</description> </chassis></chassis-inventory>');
 


select data_xml from xml_test where data_xml is document;

select (xpath('/chassis-inventory/chassis/serial-number/text()',       data_xml,       ARRAY[ARRAY['junos',
'http://xml.juniper.net/junos/9.6R4/junos-chassis']]      )) from xml_test;

ROLLBACK;


This gives me the following:


BEGIN
CREATE TABLE
INSERT 0 1                                  data_xml
------------------------------------------------------------------------------- <chassis-inventory
xmlns="http://xml.juniper.net/junos/9.6R4/junos-chassis">+  <chassis junos:style="inventory">
             +     <name>Chassis</name>                                                    +
<serial-number>JN1111111111</serial-number>                            +     <description>MX960</description>
                            +   </chassis>                                                                +
</chassis-inventory>
(1 row)
xpath
-------{}
(1 row)

ROLLBACK


Can anyone suggest how I would go about getting the serial-number with xpath?

Thanks