Hosts MUST provide an interface to the DNS for all application programs running on the host. This interface will typically direct requests to a system process to perform the resolver function [DNS:1, 6.1:2].
At a minimum, the basic interface MUST support a request for all information of a specific type and class associated with a specific name, and it MUST return either all of the requested information, a hard error code, or a soft error indication. When there is no error, the basic interface returns the complete response information without modification, deletion, or ordering, so that the basic interface will not need to be changed to accommodate new data types.
The soft error indication is an essential part of the interface, since it may not always be possible to access particular information from the DNS; see Section 188.8.131.52.
A host MAY provide other DNS interfaces tailored to particular functions, transforming the raw domain data into formats more suited to these functions. In particular, a host MUST provide a DNS interface to facilitate translation between host addresses and host names.