1. Introduction

   The purpose of this document is to define a new, straightforward
   Dynamic Delegation Discovery Service (DDDS) [7] application to allow
   mapping of domain names to URIs for particular application services
   and protocols.  This allows the "lookup" of particular services
   available for given domains, for example.

   Although this is defining a new and separate DDDS Application, dubbed
   U-NAPTR, it is built from the same principles as the Straightforward
   NAPTR (S-NAPTR) application, specified in [2].  This specification is
   not an update of S-NAPTR, but the reader is encouraged to review that
   document for extensive coverage of motivation and implementation
   considerations.

   S-NAPTR provides for application service location that does not rely
   on rigid domain naming conventions.  It is deemed "straightforward"
   in part because it rules out the use of regular expressions in NAPTR
   records (for the S-NAPTR DDDS Application).  However, that also rules
   out the possibility of providing a URI as the target of DDDS
   resolution.  A number of applications, specified (e.g., [9]) and
   proposed, find the restriction too limiting, making S-NAPTR a near
   miss to suit their needs.

   This U-NAPTR is effectively a modest extension to S-NAPTR, to
   accommodate the use of URIs as targets, without allowing the full
   range of possible regular expressions in NAPTR records.