rel-tag-ja
rel-tag
仕様ドラフト 2005-01-10
編者/作者
原案
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。
rel-tagの意図、範囲
rel-tagはWebページ（又はその一部）に「タグ付け」をする目的で作られました。このため、任意のURLやページ外部のコンテンツに対し、rel-tagによりタグ付けを行える様にはできていません。URLのタグ付けは考えるべきトピックでありますが、rel-tagにおいてその議論はなされるべきでないと考えています。xFolkやhReviewにてURLのタグ付けについて考えられているので、そちらを参照してください。
XMDPプロファイル
<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.
- Nutch has a rel-tag parser committed to their svn repository.
- Dreamweaver Extension suite from the Web Standards Project enables rel-tagging from within Dreamweaver 8.
- Scooch slide show creator allows authors to generate rel-tags and group slide shows by rel-tag via a list or cloud with tag usage count.
- The Freetag plugin for the Serendipity blog software supports rel-tags on a per-entry basis, as well as inside of its tag clouds. (The Freetag plugin is available inside of SPARTACUS)
- pnh_mf is a plugin for Textpattern that supports embedding rel-tags and other microformats in templates and blog posts. Written by Chris Casciano.
- tru_tags is a plugin for Textpattern that supports rel-tagging blog posts via the Keywords field.
- LiveJournal - see also their FAQ regarding their tags support
- TagsLinks Turn each tag into links that let you find related content on tagging services.
- ODEO publishes rel-tags for user entered tags.
- EVDB publishes rel-tags for user entered tags.
- Tag plugin for WordPress
- Tag plugin for Blosxom
- Technorati first implemented rel-tag in its Technorati Tags service. Technorati indexes rel-tag tags.
- Greasemonkey script for Firefox that generates tags for Blogger
References
Normative References
- HTML 4
- XHTML 1
- XMDP
- RFC 3986 specifies URL syntax. Section 3.3 specifies URL paths and path segments.
Informative References
- hReview uses rel-tag for tags and scalar tags
- xFolk uses rel-tag to build a distributed remote resource tagging construct
- Attention.XML uses rel-tag for reader tagging of pages, posts, feeds
- hCard can use rel-tag for categories
- hCalendar can use rel-tag for categories
- Using Technorati Tags
- Contributed from http://developers.technorati.com/wiki/RelTag
Discussions
- フィードバックはrel-tag-feedbackにてお願いします。
- rel-tagについて言及しているページも参照してください。
- これまでの経緯についてはDerek PowazekによるHow Tags Happened at Technoratiをお読み下さい。
Q&A
- rel-tagに関して分からないことがありますか？それがrel属性に関する疑問ならばrel FAQを、rel-tagに関する疑問であればrel-tag FAQをお読み下さい。これらのページを読んでも疑問が解消されない場合は、microformats-discussにメールを投稿するとよいでしょう。
Issues
- rel-tagの仕様に問題点を見つけた場合は、rel-tag issuesにて報告してください。