OpenFlow is a well-known southbound API. OpenFlow defines the way the SDN Controller should interact with the forwarding plane to make adjustments to the network, so it can better adapt to changing business requirements.
The Network Configuration Protocol (NetConf) uses Extensible Markup Language (XML) to install, manipulate and delete configuration to network devices.

Cisco Community - Difference between logging level and logging facility Post by ahmednaas
"The logging facility command basically tells the syslog server where to put the log message. You configure the syslog server with something like:
local7.debug /var/adm/local7.log
Now, when you use the "logging facility local7" on your device, all messages with severity "debug" or greater should be saved in /var/adm/local7.log." Example: on a switch, any process (CDP, SNMP, etc.) can generate a log message. On a syslog server, the logging facility is the place where all received messages with the same priority level are stored.