performing calculations with values in xml CLOB which has identical tags using sql

[vyemen]

I've got a table (event_archive) and one of the columns(event_xml) has CLOB data in xml format as below. Is there a way to use SQL to summate the values of the "xx" tag? Please help as i'm completely baffled. Even simply extracting the values is a problem as there are 2 "xx" tags within the same root. Thanks in advance.\[code\]<?xml version="1.0" encoding="UTF-8"?><event type="CALCULATION"><source_id>INTERNAL</source_id><source_participant/><source_role/><source_start_pos>1</source_start_pos><destination_participant/><destination_role/><event_id>123456</event_id><payload><cash_point reference="abc12345"><adv_start>20120907</adv_start><adv_end>20120909</adv_end><conf>1234</conf><profile>3</profile><group>A</group><patterns><pattern id="00112"><xx>143554.1</xx><yyy>96281.6</yyy><adv>875</adv></pattern><pattern id="00120"><xx>227606.1</xx><yyy>97539.8</yyy><adv>18181</adv></pattern></patterns></cash_point></payload></event>\[/code\]