"This document describes a Dynamic Delegation Discovery System (DDDS) Database using the Domain Name System (DNS) as a distributed database of Rules. The Keys are domain-names and the Rules are encoded using the Naming Authority Pointer (NAPTR) Resource Record (RR). Since this document obsoletes RFC 2915@ it is the official specification for the NAPTR DNS Resource Record. It is also part of a series that is completely specified in ""Dynamic Delegation Discovery System (DDDS) Part One: The Comprehensive DDDS"" (RFC 3401). It is very important to note that it is impossible to read and understand any document in this series without reading the others."
RFC 3403-2002 history
2002RFC 3403-2002 Dynamic Delegation Discovery System (DDDS) Part Three: The Domain Name System (DNS) Database