--http://www.quest.com/whitepaper/how-to-use-sql-servers-extended-events-and-notifications816315.aspx

;WITH SystemHealth
AS (
	SELECT 
		CAST ( target_data AS xml ) AS SessionXML
	FROM 
		sys.dm_xe_session_targets st
	INNER JOIN 
		sys.dm_xe_sessions s 
	ON 
		s.[address] = st.event_session_address
	WHERE 
		name = 'system_health'
)
SELECT 
	Deadlock.value ( '@timestamp', 'datetime' ) AS DeadlockDateTime
,	CAST ( Deadlock.value ( '(data/value)[1]', 'Nvarchar(max)' ) AS XML ) AS DeadlockGraph
FROM 
	SystemHealth s
CROSS APPLY 
	SessionXML.nodes ( '//RingBufferTarget/event' ) AS t (Deadlock)
WHERE 
	Deadlock.value ( '@name', 'nvarchar(128)' ) = N'xml_deadlock_report'
ORDER BY
	Deadlock.value ( '@timestamp', 'datetime' );