The primary goal of RFC 1592 is to specify the SNMP DPI. This is a protocol by which subagents can exchange SNMP related information with an agent. On top of this protocol, one can imagine one or possibly many Application Programming Interfaces, but those are not addressed in RFC 1592.
In order to provide an environment that is generally platform independent, RFC 1592 strongly suggests that you also define a DPI API. There is a sample DPI API available in the RFC. The document describes the same sample API as the IBM supported DPI Version 2.0 API, see A DPI Subagent Example.