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[14] [[電子ニュース]]のメッセージ形式 ([[Usefor]])
の[[頭欄]]、 [DFN[[CODE(822)[[[Distribution]]]]:]] 欄には、
そのメッセージの配布範囲 (の希望) を記述します。

たとえば、 [SAMP(822)[Distribution: [[world]]]]
は、世界中に配布 (してもよい) ことを表します。
[SAMP(822)[Distribution: [[local]]]] は、局所的に配布して欲しい
(そのサイト内だけで、他のサイトには配送して欲しくない)
ことを表します。

* Distribution: の値 (配布範囲名)

[15]
あまり上手く機能していないので、使われない(使わないようにしようとする)
傾向にあります。

world が既定値的に扱われています。 local が自分のホストだけを指す
名前としてよく使われます。その他の名前は各ホストの設定次第です。

[20] 
日本では [[fj.*]] への投稿で fj という名前が良く使われていましたが、
意味が無いので止めようということになりました (がまだつけている
人もいるとかいないとか)。

draft-usefor-article では先頭に「!」をつけることでその範囲を除外できる
としています。

また、「all」の使用を禁じ、配布範囲名は3文字以上とし、
2文字の名前は国名と見なすとしています。

** 広域的な値

,*値	,*意味	,*説明・仕様
,ca
,can	,カナダ	,>>8
,eunet	,EUNET (≒欧州)
,fj	,fj.* 配送範囲	,>>3
,inet	,Internet
,la
,local	,local	,>>2
,mtl	,Montreal	,>>8
,na	,北米	,>>8
,nippon	,nippon.* 配送範囲	,>>1
,nj	,New Jersey	,[RFC 1036]
,ny	,	,[RFC 1036]
,ont	,Ontario	,>>10
,qc	,Quebec	,>>8
,to
,tor
,tx
,uk	,連合王国	,
,us	,アメリカ合衆国	,[[usefor-article]]
,uwo	,UWO 関連サイト	,>>10
,world	,全世界	,既定値。 >>4

注: [CODE[local]] に相当する範囲名は上の表には載せていない。
>>5- を参照。

[2] [CODE[local]] は、ローカル・サイトのみ配布します。
投稿したサーバーのみ又は投稿したサーバーの属する組織内のみ配布されるのが普通です。

[4] [CODE[world]] は世界中に配布します。

[3] [CODE[fj]] は、 [[fj.*]] に記事を投稿する時に慣習的につけていましたが、
1995〜6年頃意味が無いからやめようと言われだされ、その後徐々に減り、やがて書くことが間違いとされ、今ではほとんど見かけません。
[CODE[Distribution:]] が [[Newsgroups:]] のように使われていた時代の名残とも言われています。
(真偽はしらん。)

[12] 米国・カナダの州についてはその2文字略称が使われています。

- [1] ''The nippon Newsgroups'' <http://www.gcd.org/news/nippon/Welcome.ja.html>
- [10] ''Usenet News Service: Distribution Codes'' <http://www.uwo.ca/its/news/distrib.html>
[[#comment]]

** local 相当の値

- [5] ''ニュースの投稿'' <http://web.icc.u-tokai.ac.jp/question/unix/news/mnewsns.html>: [CODE[u-tokai]] (東海大学), [CODE[yunoki]] (東海大及び静岡短大)
- [6] [CODE[imasy]] (imasy.or.jp): ''UUCPのニュース初期設定ガイド'' <http://www.imasy.or.jp/faq/txt/INIT_USER_NEWS_SETUP_PROPOSAL>
- [7] [CODE[spd]]: ''Linuxの管理を効率的に'' <http://member.nifty.ne.jp/maaberu/kanri.htm>
- [8] [CODE[concordia]] (Concordia 大): ''Netnews: the "Distribution" Header'' <http://newsflash.concordia.ca/public/faqs/distribution.html>

** トップ・カテゴリと同じ値

- [11] [CODE[sdnet]], [CODE[sub]], [CODE[dnet]], [CODE[fj]], [CODE[japan]], [CODE[no]]
- [13] [CODE[comp]]

* 関連

[21] [CODE[Newsgroups:]] で指定する[[ニュースグループ]]と直交する概念で、
話題と地域で記事の流通範囲を制御できるという面白い仕組みだったのですが、
うまく運用するのは難しかったようですね。

[22] 
同じグループに投稿しているのにこの記事はみんなに見える、
この記事はA地域に見える、
この記事はB地域 (A地域を包含する。) に見える、
この記事はC大学に見える、
とわかれていると返信が想定する相手に届くかもわかりにくそうです。
先日のこの記事にもありましたよね、と参照しても相手がそもそも知らないという事態も起こりますし。

* 歴史

** RFC 1036

[FIG(quote)[ [18] [[RFC 1036]] (Usefor) 2.2.7.  Distribution

[PRE[
    This line is used to alter the distribution scope of the message.
    It is a comma separated list similar to the "Newsgroups" line.  User
    subscriptions are still controlled by "Newsgroups", but the message
    is sent to all systems subscribing to the newsgroups on the
    "Distribution" line in addition to the "Newsgroups" line.  For the
    message to be transmitted, the receiving site must normally receive
    one of the specified newsgroups AND must receive one of the
    specified distributions.  Thus, a message concerning a car for sale
    in New Jersey might have headers including:
]PRE]

[PRE[
                   Newsgroups: rec.auto,misc.forsale
                   Distribution: nj,ny
]PRE]

[PRE[
    so that it would only go to persons subscribing to rec.auto or misc.
    for sale within New Jersey or New York.  The intent of this header
    is to restrict the distribution of a newsgroup further, not to
    increase it.  A local newsgroup, such as nj.crazy-eddie, will
    probably not be propagated by hosts outside New Jersey that do not
    show such a newsgroup as valid.  A follow-up message should default
    to the same "Distribution" line as the original message, but the
    user can change it to a more limited one, or escalate the
    distribution if it was originally restricted and a more widely
    distributed reply is appropriate.
]PRE]

]FIG]

** son-of-RFC1036

[FIG(quote)[ [23] 6.7. Distribution

The Distribution  header  content  specifies  geographic  or
          organizational limits on an article's propagation:

Distribution-content  = distribution *( dist-delim distribution )
               dist-delim            = ","
               distribution          = plain-component

A distribution is syntactically identical to a one-component
newsgroup name, and must satisfy the same rules and restrictions.   
In the absence of Distribution, the default distribution is "world".

配布は構文的には部品1つの新聞組名と同じで、同じ規則と制限を
満たさなければなりません。 Distribution が指定されていない場合の
既定値は「world」(世界)です。

NOTE: This syntax has the disadvantage of contain-
               ing  no  white space, making it impossible to con-
               tinue a Distribution header across several  lines.
               Implementors  of  relayers  and reading agents are
               warned that it is intended that the  successor  to
               this  Draft  will  change  the  definition of dist
               delimiter to:

dist-delim = "," [ space ]

and are urged to  fix  their  software  to  handle
               (i.e., ignore) white space following the commas.

A relayer MUST not pass an article to another relayer unless
          configuration information  specifies  transmission  to  that
          other  relayer  of  BOTH  (a)  at least one of the article's
          newsgroup(s), and (b) at least one of the article's  distri-
          bution(s).   In effect, the only role of distributions is to
          limit propagation, by preventing  transmission  of  articles
          that would have been transmitted had the decision been based
          solely on newsgroups.

A posting agent might wish to present  a  menu  of  possible
          distributions, or suggest a default, but normally SHOULD not
          supply a default without giving the poster a chance to over-
          ride  it.  A followup agent SHOULD initially supply the same
          Distribution header as found in the precursor, although  the
          poster MAY alter this if appropriate.

Despite  the syntactic similarity and some historical confu-
          sion, distributions are  NOT  newsgroup  names.   The  whole
          point  of putting a distribution on an article is that it is
          DIFFERENT from the newsgroup(s).  In general,  a  meaningful
          distribution  corresponds to some sort of region of propaga-
          tion: a geographical area, an organization, or a cooperating
          subnet.

NOTE:  Distributions  have  historically  suffered
               from the completely uncontrolled nature  of  their
               name  space,  the  lack  of feedback to posters on
               incomplete propagation resulting from use of  ran-
               dom  trash  in Distribution headers, and confusion
               with  newsgroups  (arising  partly  because   many
               regions  and  organizations DO have internal news-
               groups with names resembling their  internal  dis-
               tributions).  This has resulted in much garbage in
               Distribution headers, notably the pointless  prac-
               tice  of  automatically supplying the first compo-
               nent of  the  newsgroup  name  as  a  distribution
               (which is MOST unlikely to restrict propagation!).
               Many sites have opted to maximize  propagation  of
               such  ill-formed  articles by essentially ignoring
               distributions.  This unfortunately interferes with
               legitimate uses.  The situation is bad enough that
               distributions must be considered  largely  useless
               except  within  cooperating  subnets  that make an
               organized effort to restrain propagation of  their
               internal distributions.

NOTE:  The  distributions "world" and "local" have
               no standard magic meaning (except that the  former
               is  the  default  distribution  if none is given).
               Some pieces of software do assign such meanings to
               them.

参考: 配布範囲「world」及び「local」(局地)には、(前者が省略時の
既定配布範囲であることを除いて)標準的な特別な意味はありません。
これに特別な意味を与えるソフトウェアもあります。

]FIG]

** usefor-article

[FIG(quote)[ [19] [[draft-ietf-usefor-article-06]] (Usefor) 6.6.  Distribution

[PRE[
   The Distribution header is an inheritable header (see 4.2.2.2) which
   specifies geographical or organizational limits to an article's
   propagation.
]PRE]

[PRE[
      Distribution-content= distribution *( dist-delim distribution )
      dist-delim          = ","
      distribution        = positive-distribution /
                               negative-distribution
      positive-distribution
                          = *FWS distribution-name *FWS
      negative-distribution
                          = *FWS "!" distribution-name *FWS
      distribution-name   = ALPHA 1*distribution-rest
      distribution-rest   = ALPHA / "+" / "-" / "_"
]PRE]

[PRE[
        NOTE: The use of ALPHA in the syntax ensures that distribution
        names are always in US-ASCII.
]PRE]

[PRE[
   Articles MUST NOT be passed between relaying agents or to serving
   agents unless the sending agent has been configured to supply and the
   receiving agent to receive BOTH of
       (a) at least one of the newsgroups in the article's Newsgroups
       header, and
       (b) at least one of the positive-distributions (if any) in the
       article's Distribution header and none of the negative-
       distributions.
   Additionally, reading agents MAY be configured so that unwanted
   distributions do not get displayed.
]PRE]

[PRE[
        NOTE: Although it would seem redundant to filter out unwanted
        distributions at both ends of a relaying link (and it is clearly
        more efficient to do so at the sending end), many sending sites
        have been reluctant, historically speaking, to apply such
        filters (except to ensure that distributions local to their own
        site or cooperating subnet did not escape); moreover they tended
        to configure their filters on an "all but those listed" basis,
        so that new and hitherto unheard of distributions would not be
        caught. Indeed many "hub" sites actually wanted to receive all
        possible distributions so that they could feed on to their
        clients in all possible geographical (or organizational)
        regions.
]PRE]

[PRE[
        Therefore, it is desirable to provide facilities for rejecting
        unwanted distributions at the receiving end. Indeed, it may be
        simpler to do so locally than to inform each sending site of
        what is required, especially in the case of specialized
        distributions (for example for control messages, such as cancels
        from certain issuers) which might need to be added at short
        notice.  Tha possibility for reading agents to filter
        distributions has been provided for the same reason.
]PRE]

[PRE[
   Exceptionally, ALL relaying agents are deemed willing to supply or
   accept the distribution "world", and NO relaying agent should supply
   or accept the distribution "local".  However, "world" SHOULD NEVER be
   mentioned explicitly since it is the default when the Distribution
   header is absent entirely.  "All" MUST NOT be used as a
   distribution-name.  Distribution-names SHOULD contain at least three
   characters, except when they are two-letter country names as in [ISO
   3166].  Distribution-names are case-insensitive (i.e. "US", "Us" and
   "us" all specify the same distribution).
]PRE]

[PRE[
        NOTE: "Distribution: !us" can be used to cause an article to go
        to the whole of "world" except for "us".
]PRE]

[PRE[
   Posting agents Ought Not to provide a default Distribution header
   without giving the poster an opportunity to override it. Followup
   agents SHOULD initially supply the same Distribution header as found
   in the precursor.
]PRE]

]FIG]

[16] [CITE@en[RFC 5537 - Netnews Architecture and Protocols]]
( ([TIME[2014-09-14 17:08:11 +09:00]] 版))
<http://tools.ietf.org/html/rfc5537#page-15>

[17] [CITE@en[RFC 5536 - Netnews Article Format]]
( ([TIME[2014-09-21 18:14:06 +09:00]] 版))
<http://tools.ietf.org/html/rfc5536#section-3.2.4>

* メモ

- [9] ''Distribution'' <http://www.templetons.com/usenet-format/distr.html>

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