How can Enterprise Manager 12c Cloud Control self-service chargeback metering data be accessed by external billing systems?

By using an RSS feed from the Chargeback home page 

By defining the external billing system as an Enterprise Manager target that may connect to the Chargeback application 

By running emcli get_metering_data and importing the output into the billing system as required 

By defining the external billing system as an Enterprise Manager target that then uses a 81 Publisher report to obtain the billing data