SID_XDB service and SID_XPT Service 

In oracle 10g, when you check the listener service, you may notice two particular services registered:
[ccbqa] /orasw/app/oracle/admin/ >lsnrctl status|grep ccbqa
Service "ccbqa" has 1 instance(s).
  Instance "ccbqa", status READY, has 1 handler(s) for this service...
Service "ccbqaXDB" has 1 instance(s).
  Instance "ccbqa", status READY, has 1 handler(s) for this service...
Service "ccbqa_XPT" has 1 instance(s).
  Instance "ccbqa", status READY, has 1 handler(s) for this service...