rel-tag-ja

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rel-tag

仕様ドラフト 2005-01-10

編者/作者

Tantek Çelik

原案

Derek Powazek Kevin Marks

著作権

This specification is (C) 2004-2024 by the authors. However, the authors intend to submit (or already have submitted, see details in the spec) this specification to a standards body with a liberal copyright/licensing policy such as the GMPG, IETF, and/or W3C. Anyone wishing to contribute should read their copyright principles, policies and licenses (e.g. the GMPG Principles) and agree to them, including licensing of all contributions under all required licenses (e.g. CC-by 1.0 and later), before contributing.

特許

この仕様はロイヤリティーフリーの特許方針に帰属するものです。特許方針に関してはW3C Patent PolicyやRFC3667、RFC3668をご覧下さい。

概要

rel-tagはmicroformatsのひとつです。ハイパーリンクにrel="tag"を書き加える事により、リンク元のページに対しページ作者が定義した「タグ（キーワードやテーマ）」を関連づけることができます。 タグはblogの記事内容すべてに関係する言葉とは限りません。たとえば次のようなリンクでタグを関連づけるとします。 

<a href="http://technorati.com/tag/tech" rel="tag">tech</a>

これは作者がこのWebページ（または内容の一部）に「tech」というタグをつけていることを意味します。

リンク先のページはWeb上に存在するべき（SHOULD）であり、またタグの意味はリンクテキストの内容よりも、リンク先のページが持つ情報が優先されます。たとえば次のようなマークアップでページに対しタグ付けを行ったとします。 

<a href="http://technorati.com/tag/tech" rel="tag">fish</a>

URLの最後にある単語がタグの意味として扱われるので、この場合ページのタグは「fish」ではなく「tech」となります。

Scope

rel="tag" is specifically designed for "tagging" content, typically web pages (or portions thereof, like blog posts).

rel="tag" is NOT designed for "tagging" arbitrary URLs or external content. There is demand for a general decentralized syntax for tagging URLs, and that is certainly something to think about, but this is not meant for that. See xFolk and hReview for ways to tag arbitrary URLs.

XMDP profile

<dl class="profile">
 <dt id="rel">rel</dt>
 <dd><p>
   <a rel="help" href="http://www.w3.org/TR/html401/struct/links.html#adef-rel">
     HTML4 definition of the 'rel' attribute.</a>  
   Here is an additional value.</p>
  <dl>
   <dt id="tag">tag</dt>
   <dd>Indicates that the referred resource serves as a "tag", 
       or keyword/subject, for the referring page.</dd>
  </dl>
 </dd>
</dl>

Tag Spaces

Tags are embedded in HTTP URIs in a well-defined manner so that the tag embedded in an HTTP URI can be mechanically extracted from that URI. Specifically, the last segment of the path portion of the URI (after the final "/" character) contains the tag value. For example, the URI 

http://www.example.com/tags/foo

contains the tag "foo".

Thus, for the purposes of comparing two HTTP URIs as tags, the last segment of the path portion should be extracted and only that value (that value of the tag) should be compared.

Need more formal language about comparison and extraction process.

The destination of a rel="tag" hyperlink is required to be a tag space (a place that collates or defines tags), where the last segment of the path of the URL is the tag, e.g. 

http://technorati.com/tag/tech

is a URL for the tag "tech".

Tags may only be placed in the URL path, and only in the last segment of the path. Tags may not be placed in query parameters or fragment identifiers. e.g. 

http://technorati.com/tag/tech?tag=fish#emu

is still a URL for the tag "tech", not "fish" or "emu".

Since the only part of a tag space URL of which any structure is required is the last path segment, a tag space URL can be hosted at any domain. Authors may choose to link to a tag at a particular tag space in order to provide a specific meaning. E.g. a tag for technology could link to: 

  http://en.wikipedia.org/wiki/Technology

Trailing slashes in tag URLs are ignored, that is: 

  http://technorati.com/tag/Technology/

as a rel-tag URL is treated as: 

  http://technorati.com/tag/Technology

Encoding issues

Spaces can be encoded either as + or %20. Unicode characters are encoded as specified in RFC 3986. For example: 

<a href="http://technorati.com/tag/Sant%C3%A9+et+bien-%C3%AAtre" rel="tag">Santé et bien-être</a>

Note that if using Wikipedia as a tagspace, as discussed above, you should use %20 as they remap '+' to %2B, causing a page with a plus sign in the title (which usually does not exist) to appear.

Tags Are Visible Metadata

rel="tag" hyperlinks are intended to be visible links on pages and posts. This is in stark contrast to meta keywords (which were invisible and typically never revealed to readers), and thus is at least somewhat more resilient to the problems which plagued meta keywords.

Making tag hyperlinks visible has the additional benefit of making it more obvious to readers if a page is abusing tag links, and thus providing more peer pressure for better behavior. It also makes it more obvious to authors, who may not always be aware what invisible metadata is being generated on their behalf.

As a result the invisible tag link syntax variant: <link rel="tag" href="..." /> SHOULD NOT be supported by implementations.

Implementations

This section is informative.

The following implementations have been developed which either generate or parse rel-tag links. If you have a rel-tag implementation, feel free to add it to the top of this list. Once the list grows too big, we'll make a separate wiki page.

References

Normative References

  • HTML 4
  • XHTML 1
  • XMDP
  • RFC 3986 specifies URL syntax. Section 3.3 specifies URL paths and path segments.

Informative References

Discussions

Q&A

  • If you have any questions about rel-tag, check the rel FAQ first for general rel attribute questions, then check the rel-tag FAQ, and then if you don't find answers, ask your question on the microformats-discuss mailing list.

Issues

  • Please add any issues with the specification to the separate rel-tag issues document.
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