rel-tag

2007-03-19T18:16:54Z

HubTag: Added a new implementation - rel-tag links are supported in the technorati search tag and in the email sent to site users

<h1> rel-tag </h1>

__TOC__

== Draft Specification 2005-01-10 ==
=== Editors/Authors ===
[http://tantek.com/ Tantek Çelik]

[http://epeus.blogspot.com/ Kevin Marks]

=== Concept ===
[http://powazek.com/ Derek Powazek]

=== Copyright ===
{{MicroFormatCopyrightStatement2004}}

=== Patents ===
{{MicroFormatPatentStatement}}

== Abstract ==
[[Rel-Tag]] is one of several [[MicroFormats]]. By adding <code>rel="tag"</code> to a hyperlink, a page indicates that the destination of that hyperlink is an author-designated "tag" (or keyword/subject) for the current page. Note that a tag may just refer to a major portion of the current page (i.e. a blog post). e.g. by placing this link on a page,

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

the author indicates that the page (or some portion of the page) has the tag "tech".

The linked page SHOULD exist, and it is the linked page, rather than the link text, that defines the tag. The last path component of the URL
is the text of the tag, so

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

would indicate the tag "tech" rather than "fish".

== 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 external to the current page, but this is not meant for that. See [[xfolk|xFolk]] and [[hreview|hReview]] for ways to tag arbitrary URLs.

If you need to define tags as part of a more specialised format, rel="tag" is the recommended way to do so, and [[xfolk|xFolk]], [[hreview|hReview]], [[hcard |hCard]] and [[hcalendar|hCalendar]] all do this.
== XMDP profile ==
<pre><nowiki>
<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>
</nowiki></pre>

== 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 <pre><nowiki>http://www.example.com/tags/foo</nowiki></pre> 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.

<pre><nowiki>http://technorati.com/tag/tech </nowiki></pre>

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.

<pre><nowiki>http://technorati.com/tag/tech?tag=fish#emu </nowiki></pre>

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:

<pre><nowiki> http://en.wikipedia.org/wiki/Technology </nowiki></pre>

Trailing slashes in tag URLs are ignored, that is:

<pre><nowiki> http://technorati.com/tag/Technology/ </nowiki></pre>
as a rel-tag URL is treated as:
<pre><nowiki> http://technorati.com/tag/Technology </nowiki></pre>

== Encoding issues ==
Spaces can be encoded either as <code>+</code> or <code>%20</code>. Unicode characters are encoded as specified in [http://www.ietf.org/rfc/rfc3986.txt RFC 3986]. For example:

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

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

== Tags Are Visible Metadata ==
<code>rel="tag"</code> 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: <code><link rel="tag" href="..." /></code> SHOULD NOT be supported by implementations.

==Examples in the Wild==
This section is '''informative'''.

The following sites have implemented rel-tag, and thus are a great place to start for anyone looking for examples "in the wild" to try parsing, indexing, organizing etc. If your site marked up with rel-tag, feel free to add it to the '''top''' of this list. Once the list grows too big, we'll make a separate wiki page.

* [http://www.international.unt.edu UNT International] uses rel-tag to indicate content categories on most pages
* [http://yedda.com Yedda] - Yedda publishes rel-tags for all of the tags the people entered on themselves as well as on all tags entered on questions asked on Yedda.
* [http://www.lingr.com Lingr] publishes rel-tags for all user entered tags.
* [http://odeo.com ODEO] [http://odeo.com/blog/2005/07/adding-microformats-to-odeo.html publishes] rel-tags for user entered tags.
* [http://eventful.com Eventful] publishes rel-tags for user entered tags.

== 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.

* [http://www.hubtag.com HubTag] helps users find a unique tag across the web for their event - eg. JohnAndBettysWeddingWimbledonMarch07
* [http://www.necctar.com Necctar] is a search engine exclusively based on tag microformat parsing and processing. Necctar uses tags entered by bloggers to index the world wide web
* Nutch has a [[rel-tag]] parser [http://www.mail-archive.com/nutch-commits@lucene.apache.org/msg01014.html committed to their svn repository].
* [http://www.webstandards.org/action/dwtf/microformats/ Dreamweaver Extension suite] from the [http://webstandards.org/ Web Standards Project] enables rel-tagging from within Dreamweaver 8.
* [http://scooch.gr0w.com/ 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 [http://www.s9y.org 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)
* [http://placenamehere.com/TXP/pnh_mf/ pnh_mf] is a plugin for [http://textpattern.com/ Textpattern] that supports embedding rel-tags and other microformats in templates and blog posts. Written by [http://placenamehere.com/ Chris Casciano].
* [http://www.truist.com/blog/493/trutags-a-tagging-plugin-for-textpattern tru_tags] is a plugin for [http://textpattern.com/ Textpattern] that supports rel-tagging blog posts via the Keywords field.
* [http://news.livejournal.com/86492.html?thread=24881884 LiveJournal] - see also [http://www.livejournal.com/support/faq.bml?cat=tags their FAQ regarding their tags support]
* [http://trac.labnotes.org/cgi-bin/trac.cgi/wiki/TagsLinks TagsLinks] Turn each tag into links that let you find related content on tagging services.
* [http://dev.wp-plugins.org/wiki/BunnysTechnoratiTags Tag plugin for WordPress]
** Note that some sites using WordPress (http://microformatique.com/ for instance) are getting incorrect tags. The tag is ?cat=12 instead of the actual tag value.
* [http://noone.org/blog/tags/Tagging Tag plugin for Blosxom]
* Technorati first implemented rel-tag in its [http://technorati.com/tag/ Technorati Tags] service. Technorati indexes rel-tag tags.
* [http://consumingexperience.blogspot.com/2005/12/updated-multiple-word-technorati-tag.html Greasemonkey script for Firefox that generates tags for Blogger]
* [http://tools.microformatic.com/help/xhtml/rel-lint/ rel-lint] is a validation tool by [[User:DrewMcLellan|Drew McLellan]] that will validate existence of rel-tag attributes.

== References ==
=== Normative References ===
* [http://www.w3.org/TR/REC-html40/ HTML 4]
* [http://www.w3.org/TR/xhtml1/ XHTML 1]
* [http://gmpg.org/xmdp/ XMDP]
* RFC 3986 specifies URL syntax. Section 3.3 specifies URL paths and path segments.

=== Informative References ===
* [[hreview|hReview]] uses rel-tag for tags and scalar tags
* [[xfolk|xFolk]] uses rel-tag to build a distributed remote resource tagging construct
* [http://developers.technorati.com/wiki/attentionxml Attention.XML] uses rel-tag for reader tagging of pages, posts, feeds
* [[hcard|hCard]] can use rel-tag for categories
* [[hcalendar|hCalendar]] can use rel-tag for categories
* [http://technorati.com/help/tags.html Using Technorati Tags]
* Contributed from http://developers.technorati.com/wiki/RelTag
* [http://microformatique.com/?p=61 Know your rel-tag] at microformatique.com

== Discussions ==
* Feedback is encouraged on the [[rel-tag-feedback]] page.
* See also [http://www.technorati.com/cosmos/referer.html blogs discussing this page].
* History: [http://www.powazek.com/2005/07/000532.html How Tags Happened at Technorati] by [http://www.powazek.com/ Derek Powazek]

=== Q&A ===
* If you have any questions about rel-tag, check the [[rel-faq|rel FAQ]] first for general rel attribute questions, then check the [[rel-tag-faq|rel-tag FAQ]], and then if you don't find answers, ask your question on the [http://microformats.org/discuss microformats-discuss] mailing list.

==Related pages==
{{rel-tag-related-pages}}

Microformats Wiki - User contributions [en]

rel-tag