The Request For Comment (RFC) published by the IETF that set the standard for Domain Name Systems.

(See also: DNS) A quick exerpt:
Network Working Group                                                      P. Mockapetris
Request for Comments:  883                                                                  ISI
                                                           November 1983

            DOMAIN NAMES - IMPLEMENTATION and SPECIFICATION

        | This memo discusses the implementation of domain    |
        | name servers and resolvers, specifies the format of |
        | transactions, and discusses the use of domain names |
        | in the context of existing mail systems and other   |
        | network software.                                   |
        |                                                     |
        | This memo assumes that the reader is familiar with  |
        | RFC 882, "Domain Names - Concepts and Facilities"   |
        | which discusses the basic principles of domain      |
        | names and their use.                                |
        |                                                     |
        | The algorithms and internal data structures used in |
        | this memo are offered as suggestions rather than    |
        | requirements; implementers are free to design their |
        | own structures so long as the same external         |
        | behavior is achieved.                               |

For more info, see http://www.faqs.org/rfcs/rfc833.html