How to check active transactions in Oracle Database

DBA scripts to view active transactions in Oracle database:

SELECT S.SID,S.SERIAL#,P.SPID "SPID",S.USERNAME,S.STATUS,S.OSUSER,S.MACHINE,t.ses_addr
   FROM V$SESSION S,V$PROCESS p,v$transaction t
   WHERE S.PADDR=P.ADDR
   AND S.USERNAME IS NOT NULL
   AND S.STATUS='ACTIVE'
   and t.ses_addr=s.saddr
   ORDER BY S.USERNAME;