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Augmented BNF for Syntax Specifications: ABNF (RFC4234)

IP.com Disclosure Number: IPCOM000129258D
Original Publication Date: 2005-Oct-01
Included in the Prior Art Database: 2005-Oct-04
Document File: 17 page(s) / 27K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

D. Crocker: AUTHOR [+3]

Abstract

Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity, with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order- independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 10% of the total text.

Network Working Group                                    D. Crocker, Ed.
Request for Comments: 4234                   Brandenburg InternetWorking
Obsoletes: 2234                                               P. Overell
Category: Standards Track                                      THUS plc.
                                                            October 2005


             Augmented BNF for Syntax Specifications: ABNF

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   Internet technical specifications often need to define a formal
   syntax.  Over the years, a modified version of Backus-Naur Form
   (BNF), called Augmented BNF (ABNF), has been popular among many
   Internet specifications.  The current specification documents ABNF.
   It balances compactness and simplicity, with reasonable
   representational power.  The differences between standard BNF and
   ABNF involve naming rules, repetition, alternatives, order-
   independence, and value ranges.  This specification also supplies
   additional rule definitions and encoding for a core lexical analyzer
   of the type common to several Internet specifications.


Crocker & Overell           Standards Track                     [Page 1]
RFC 4234                          ABNF                      October 2005


Table of Contents

   1. INTRODUCTION ....................................................2
   2. RULE DEFINITION .................................................3
      2.1. Rule Naming ................................................3
      2.2. Rule Form ..................................................3
      2.3. Terminal Values ............................................4
      2.4. External Encodings .........................................5
   3. OPERATORS .......................................................6
      3.1. Concatenation:  Rule1 Rule2 ................................6
      3.2. Alternatives:  Rule1 / Rule2 ...............................6
      3.3. Incremental Alternatives: Rule1 =/ Rule2 ...................7
      3.4. Value Range Alternatives:  %c##-## .........................7
      3.5. Sequence Group:  (Rule1 Rule2) .............................8
      3.6. Variable Repetition:  *Rule .......