INTERNET DRAFT Deukyoon Kang, Shin Fang KT / NIST March 11, 1998 Guide lines for Key words use to indicate requirement levels in RFCs <draft-kang-keyword-requirement-level-00.txt> Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). This internet draft expires on September 11, 1998. Abstract In many IETF documents several key words are used to signify the requirements in the spefcification. This document defines the requirement levels imposed by these words as they should be interpreted in IETF documments. The requirement levels are basically equivalent to the ones proposed by RFC 2119. But easier to understand the strength of key words and to introduce new key words to the hierarchy of requirement levels if ever there's a need. 1. Introduction RFC 2119 addresses the use of frequently used Key words in Internet standard track documents such as MUST, MUST NOT, SHOULD, SHOULD NOT, REQURIED, SHALL, SHALL NOT, and RECOMMENDED. It makes a very good guide to Internet standards developers and Implementers in that it leads more consistent interpretation of RFCs and Drafts than without it resulting into more interoperable implementations. However, note that most of statements in Standards documents have no key word at all. More consistent interpretation of standards track documents will be possible if we agree on the interpretation of 'no key word'. In this document, the requirement level is classified into three levels which are basically equivalent to the ones proposed by RFC 2119. But easier to understand the strength of key words and to introduce new key words to the hierarchy of requirement levels if ever there's a need. In fact, three new key words, NEVER, CAN and CANNOT are introduced in this memo as well as 'no key word'. Note that the force of key words defined in this document is modified by the requirement level of the document in which they are used. Authors who follow these guidelines should incorporate this phrase near the beginning of their document. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOUD NOT", "RECOMMENDED", "MAY", "MAY NOT", "CAN", "CANNOT", and the absence of these key words in this document are to be interpreted as described in <draft-keyword-requirement-level-00.txt>. 2. Requirement Levels Requirement and Prohibition are simply referred to as Requirement in this document. For instance, MUST and SHALL NOT indicate the same requirement level. Requirement levels are classified into three levels Level 1, 2 and 3 as follows: - Level 1: Absolute requirements of the specification * The requirements shall be satisfied without exception * Key words: MUST, MUST NOT, SHALL, SHALL NOT, NEVER, CANNOT - Level 2: Recommended requirements of the specification * There may exist valid reasons in particular circumstances to ignore a particular item. But the full implications must be understood and carefully inspected before choosing a different course. * Key words: RECOMMENDED, SHOULD, SHOULD NOT, 'No key word' - Level 3: Optional Requirements * The indicated requirement may be implemented or not depending on the flavor of vendors. An implementation which does not include a particular option must be prepared to interoperate with another implementation which does include the option, though perhaps with reduced functionality and vice versa. * Key words: OPTIONAL, CAN, MAY, MAY NOT 3. References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997. 4. Authors' addresses Deukyoon Kang Korea Telecom, Korea Phone: +1 301 975 5352 E-mail: firstname.lastname@example.org Shin Fang National Institute of Standards and Technology, MD, USA Phone: +1 301 975 4294 E-mail: email@example.com * This internet draft expires on September 11, 1998.