Which language defines the structure or modeling of data for NETCONF and RESTCONF?

YAML is a human-friendly data serialization standard, but it is not the data modeling language for NETCONF and RESTCONF.

XML is a data encoding format often used with NETCONF, but it is not the language that defines the structure of the data itself.

JSON is a lightweight data-interchange format often used with RESTCONF, but it is not the language that defines the structure of the data itself.

YANG (Yet Another Next Generation) is a data modeling language used to define the structure of configuration data, state data, notifications, and RPCs for network devices. Both NETCONF and RESTCONF utilize YANG modules to specify the data that can be manipulated and retrieved, providing a standardized and human-readable way to describe network device capabilities.