More on a tagging standard.
Rel-Tag (a.k.a relTag) is a de-facto standard for tagging a specific page. Rel-Tag was defined by Tantek Çelik, following a concept from Derek Powazek and Kevin Marks. It is part of a larger collection of microformats - a wonderfully practical approach to building a practical semantic web.
To tag your page with a Rel-Tag, you just include a link and use the attribute rel="tag" on the link:
<a href="http://technorati.com/tag/sample" rel="tag">sample</a>
It doesn't matter what page the URL points to, as long as it ends with the tag name.
Incredibly simple. Paste this piece of HTML into your page, and your page is tagged, and indexed as such by services that support this convention, such as Technorati.
I do share Kevin Burton's feeling though, that the Rel-Tag specification is somewhat lacking (or, as Kevin defined it, under-specified).
Points to consider:
- Mixing Data and Representation
- relTags are easy to create by hand (at least, assuming that you know HTML). They're even easier to generate by an application that supports them (such as Zoundry). But once generated, relTags are not just metadata, they're actually part of your content. So it becomes very hard to build a tool that edits them. You might have used these links in your content. You might have moved them around. You might want to change the link text but keep the tag. It becomes messy. Last time checked the problem of separating data from representation in a practical, widely supported manner was already solved.
- Redundancy
- The tag is repeated twice, once in the URL and once in the text. Wanna bet how quickly these two get out of sync?
- Usability
- relTags are very easy to use, if you know how to access and edit your HTML. But, if you know that, there isn't much difference between editing a "<a href" tag to add the rel="tag", and between cutting and pasting a piece of XML to achieve the same goal. And if you don't know HTML, both are equally inaccessible. So, end-user usability being pretty much the same, why not choose a more robust solution?
- Tag Spaces
- According to relTag, the actual URL you use point to any page, as long as that page is a "tag space", loosely defined as "a place that collates or defines tags". The spec goes on to inst that tag spaces can be used to provide a specific meaning to the tag. What does this mean? Is it a method to tag tags? A categorization system? A meaningless technical detail? These questions are too big to be left unspecified. The obscurity of this is leading to people (e.g. me :) repeating the tags multiple times, for each one of their favorite "tag spaces" (and to some cool gizmos).
- Scope definition
- relTags are used to tag the text that includes them. They do not carry with them a scope definition, so it would be hard for tools (or people as a matter of fact) to understand if these tags refer to the entire page, or to a specific section in the page (or post in a blog).
It'd be great if a more general and robust tagging standard would support relTags for backward compatibility.
I've been playing with the tagging format I've suggested in a previous post, and found some changes that should be applied to it in order to make it more useful. But this post is already getting way too long, so more on that later :)
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