YANG (Yet Another Next Generation) is a data modeling language used to model configuration and state data for network devices and services. It is not a Cisco proprietary language; rather, it is an open standard developed by the IETF. YANG allows model developers to create custom data types, which is essential for ensuring that models accurately represent the data they are intended to configure or monitor. This flexibility in defining data types is one of the key characteristics that makes YANG a powerful tool for network modeling.
YANG models are structured in a modular fashion, which promotes reuse of models across different implementations and vendors. While YANG does structure data in an object-oriented way, the ability to create custom data types is a distinct characteristic that sets it apart from other data modeling languages.