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Network Working Group T. Hansen
Internet-Draft AT&T Laboratories
Intended status: Informational D. Crocker
Expires: August 29, 2016 Brandenburg InternetWorking
February 26, 2016


Non-Normative Synonyms in RFCs
draft-hansen-nonkeywords-non2119-04

Abstract

Specifications in RFCs contain normative keywords, as defined in RFC
2119, to signify requirements, permission or prohibitions. These
include MUST, SHOULD and MAY, which are commonly recorded in all
CAPITALS (but need not be). The RFC 2119 words are sometimes also
used with non-normative meaning; this non-normative usage can be
confusing and it is better to restrict the RFC 2119 words to be used
solely as normative directives.

Happily, natural languages permit variation in phrasing, so that
meaning can be retained without use of this otherwise-normative
vocabulary. For such situations, this document provides some
alternatives to the normative vocabulary of RFC 2119.

Status of This Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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."

This Internet-Draft will expire on August 29, 2016.

Copyright Notice

Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.





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described in the Simplified BSD License.

1. Words That Do Double Duty

To indicate a degree of requirement, permission or prohibition for an
aspect of a specification, words such as MUST, SHOULD and MAY are
defined as normative vocabulary in the formal aspects of the RFC
series [RFC2119]. However it is also natural to use them non-
normatively, in a narrative fashion. Even when this carries no
obvious potential confusion, such as within RFCs that do not invoke
the conventions of RFC 2119, non-normative use of these words in RFCs
invites confusion for the reader; their normative meaning is too
deeply ingrained in the culture of the RFC series.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are meant to reference their occurrence in [RFC2119]. The
words are not used normatively here.

Fortunately, there are other words readily available, in lieu of the
RFC 2119 words, when a non-normative meaning is intended. These
alternatives, or their equivalents, can be used instead of the
normatively-encumbered vocabulary.




















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+-------------+----------------------------------+------------------+
| RFC 2119 | When Used With This Meaning | Some Alternative |
| Word | | Word(s) |
+-------------+----------------------------------+------------------+
| MUST, | indicates that something is | needs to, |
| REQUIRED, | essential | necessary |
| SHALL | | |
| | | |
| SHOULD, | indicates that something is | ought to, |
| RECOMMENDED | strongly urged | encouraged, |
| | | suggested |
| | | |
| MAY, | indicates the possibility or | can, might |
| OPTIONAL | capability of performing an | |
| | action | |
| | | |
| | indicates permission to perform | is allowed to, |
| | an action | is permitted to |
+-------------+----------------------------------+------------------+

Because the word "NOT" (or "not") only takes on a special meaning
when it is combined with one of the RFC 2119 normative words, the
word "not" can be freely used with any of the above suggestions and
not be taken to have any separate RFC 2119 connotation. For example,
"ought not" is non-normative, while "should not" and "SHOULD NOT"
might be normative in the RFC 2119 sense.

By using these alternative wordings, authors of RFCs and internet
drafts can avoid the possibility of vocabulary (that is sometimes
used normatively) being misinterpreted.

Note that the above list of synonyms is not meant to be exhaustive;
other non-RFC-2119-normative words can, of course, also be used at
the author's discretion.

Authors who follow these guidelines might want to incorporate a
declaration about usage at the beginning of their document.

[Note to RFC Editor: please remove this paragraph before
publication.] This document can be discussed on the ietf@ietf.org
mailing list.

2. Acknowledgements

The comments from Ran Atkinson are gratefully acknowledged.






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3. IANA Considerations

This document has no IANA considerations.

4. Security Considerations

The RFC 2119 terms are frequently used to specify behavior with
security implications. The effects on security of changing something
from a "MUST" to a "needs to", or vice versa, can be very subtle, as
one can have normative meaning and the other does not. Document
authors need to take the time to consider the effects of using non-
normative verbiage as specified in this document instead of the
normative verbiage from RFC 2119.

5. Informative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.

Authors' Addresses

Tony Hansen
AT&T Laboratories
200 Laurel Ave South
Middletown, NJ 07748
USA

Phone: +1.732.420.8934
Email: tony@att.com


D. Crocker
Brandenburg InternetWorking
675 Spruce Dr.
Sunnyvale
USA

Phone: +1.408.246.8253
Email: dcrocker@bbiw.net
URI: http://bbiw.net









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