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 (1999). All Rights Reserved.

Abstract

In RFC 2533, "A Syntax for Describing Media Feature Sets", an expression format is presented for describing media feature capabilities using simple media feature tags.

RFC 2533 『媒体機能集合記述構文』では、単純な媒体機能札を使って媒体機能能力を記述するための式書式が示されています。

This memo contains two corrections to that specification: one fixes an error in the formal syntax specification, and the other fixes an error in the rules for reducing feature comparison predicates.

このメモはその仕様書について二点の修正を含んでいます。 一つは正式な構文仕様の誤りを正し、 もう一つは機能比較述語の削減の規則の誤りを正します。

Table of Contents

1. 1. Introduction ............................................2
   1. 1.1 Terminology and document conventions 2
   2. 1.2 Discussion of this document 2
2. 2. Correction to feature expression syntax .................3
3. 3. Correction to feature set matching reduction rules ......3
4. 4. Security Considerations .................................4
5. 5. References ..............................................4
6. 6. Author's Address ........................................4
7. 7. Full Copyright Statement ................................5

1. Introduction

In RFC 2533, "A Syntax for Describing Media Feature Sets" [1], an expression format is presented for describing media feature capabilities using simple media feature tags. This provides a format for message handling agents to describe the media feature content of messages that they can handle. That memo also describes an algorithm for finding the common capabilities expressed by two different feature expressions.

RFC 2533 『媒体機能集合記述構文』では、単純な媒体機能札を使って媒体機能能力を記述するための式書式が示されています。 これはメッセージ取扱いエージェントがその取扱うことができるメッセージの媒体機能内容を記述する書式を提供します。 このメモは二つの異なる機能式で表現されている共通の能力を探す算法も記述しています。

This memo contains two corrections to that specification: one fixes an error in the formal syntax specification, and the other fixes an error in the feature set matching algorithm, in the rules for reducing feature comparison predicates.

このメモはその仕様書について二点の修正を含んでいます。 一つは正式な構文仕様の誤りを正し、 もう一つは機能集合一致算法中の、機能比較述語の削減の規則の誤りを正します。

The first of these corrections affects the normative content of RFC 2533; the second affects non-normative content.

これらの修正のうち最初の方は RFC 2533 の規定内容に影響します。 二番目の方は非規定内容に影響します。

2. Correction to feature expression syntax

In section 4.1, RFC 2533 defines the syntax for a "set" expression as follows:

RFC 2533 は、 4.1節で、 set 式の構文を次のように定義しています。

• set = attr "=" "[" setentry *( "," setentry ) "]"
• setentry = value "/" range

The production for 'setentry' should read:

生成規則 setentry は、

• setentry = value / range

とするべきです。

That is: the '/' character is not a character literal, but separates two alternative forms for 'setentry'. This corrected syntax allows the set expression examples given in section 4.2.5 of RFC 2533, such as:

つまり、 / 文字は文字表記ではなく、 setentry の2つの代替形式を分離するものです。正しい構文では、 RFC 2533 に4.2.5節に示されている

       ( width=[3,4,6..17/2] )

のような集合式例が認められます。

3. Correction to feature set matching reduction rules

In section 5.8.2, "Rules for simplifying unordered values", RFC 2533 lists the following rewriting rules for simplifying feature tag comparisons with unordered values:

RFC 2533 は 5.8.2節「非順序値の単純化の規則」で、 次の非順序値の機能札比較を単純化する書き換え規則を列挙しています。

      (LE f a)  (LE f b)      -->  (LE f a),   a=b
                                   FALSE,      otherwise
      (LE f a)  (GE f b)      -->  FALSE,      a!=b
      (LE f a)  (NL f b)      -->  (LE f a)    a!=b
                                   FALSE,      otherwise
      (LE f a)  (NG f b)      -->  (LE f a),   a!=b
                                   FALSE,      otherwise

The second of these rules is incomplete, and should read:

この規則群の二番目は不完全で、

      (LE f a)  (GE f b)      -->  (LE f a),   a=b
                                   FALSE,      otherwise

であるべきです。

NOTE: implementation experience with these rules has suggested a revised feaure set matching algorithm with a more useful set of simplification rules. Apart from the change noted above, the algorithm given in RFC 2533 has been implemented and shown to work as intended, but the results generated are not always in the most convenient form. It is planned to test and publish a revised algorithm at a future date.

注意 : これらの規則の実装経験によって、 より有用な単純化規則の集合による改訂版機能集合一致算法が提案されています。 上記の変更は別として、 RFC 2533 に示された算法は実装されて意図したとおりに動くことが示されていますが、 生成される結果は必ずしも最も便利な形式ではありません。 将来改訂版算法を試験して出版することが予定されています。

4. Security Considerations

Security considerations are discussed in RFC 2533 [1] and related documents.

安全性に関しては RFC 2533 と関連文書で触れられています。

5. References

• [1] Klyne, G., "A Syntax for Describing Media Feature Sets", RFC 2533, March 1999.
• [2] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.

6. Author's Address

   Graham Klyne
   Content Technologies Ltd.
   1220 Parkview
   Arlington Business Park
   Theale
   Reading, RG7 4SA
   United Kingdom
   Phone: +44 118 930 1300
   Fax:   +44 118 930 1301
   EMail: GK@ACM.ORG

7. Full Copyright Statement

Copyright (C) The Internet Society (1999). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

See also RFCのライセンス

Acknowledgement

Funding for the RFC Editor function is currently provided by the Internet Society.

メモ

• [1] I-D 名 : <draft-ietf-conneg-feature-syntax-er>