Arve Bersvendsen

Forward and reverse link relationships

The rel="nofollow" attribute name-value pair prompted me to re-examine what link relationships really are. I found rel="nofollow" to be an exceedingly ugly hack. And I found reverse link relationships to be as exceedingly wonderful.

Forward and reverse links

The rel attribute describes a forward link. A forward link indicates that the document referenced has a special meaning to the document you are viewing. The HTML 4.01 specifcation has this to say about rel:

rel = link-types [CI]
This attribute describes the relationship from the current document to the anchor specified by the href attribute. The value of this attribute is a space-separated list of link types.

Let’s consider the document http://example.com/story.html:

<link rel="author" href="author.html" />

Which can be read as:

The referenced document author.html contains author information for the current document; story.html.

rel=”nofollow”

Now that you know what a forward link is, I can tell you why rel="nofollow" is so exceedingly ugly. Example:

<a href="http://example.com/blogspam.html" rel="nofollow">Text</a>

With the w3c definiton of rel, read as:

The referenced document http://example.com/blogspam.html contains “nofollow” information for the current document.

Which doesn’t make sense at all. What is the “nofollow” relationship? With rel="nofollow", search engines, and some high-profile bloggers have introduced the concept of processing instructions into the link relationship. If we reread my example nofollow link as it is being treated by the search engines we get:

A User Agent should not follow the link to http://example.com/blogspam.html, or index it.

This is so 1995, and no different from <center>, <blink> or any other past www atrocity. If one wanted to introduce the idea of a link being untrusted, one should have said just that: The following link is untrusted:

<a href="http://example.com/blogspam.html" rel="untrusted">Text</a>

Reverse link relationships

Oh, these are wonderful. Let’s read the HTML 4.01 definition:

rev = link-types
This attribute is used to describe a reverse link from the anchor specified by the href attribute to the current document. The value of this attribute is a space-separated list of link types.

If we have two documents, a.html and b.html, that are part of a sequence of documents (such as the archetypal weblog entries), a.html could contain:

<link rel="next" href="b.html" />

And b.html could contain

<link rel="previous" href="a.html" />

Not only that, “b.html” could also indicate that it indeed is the “next” document for “a.html” by adding this:

<link rev="next" href="a.html" />

Read as:

This document is the “next” document for the document a.html.

However, using previous and next examples aren’t all that useful, since we already have previous and next forward link relationships. If we instead look at search results, it starts making sense. Imagine that you have written an entry about link relationships in HTML, and someone searching Google for link relationships and html found your document and visited it. Let’s also assert that your weblog system is able to find and store incoming links from Google. You could then add something like this:

<link
  rev="search"
  href="http://www.google.com/search?q=link+relationships+html"
/>

Which can be read as:

The current document is a search result for the Google search query linked to in the href attribute.

Another example, which perhaps may be easier for weblogs to add, is for Pingbacks and TrackBacks. Usually, anyone who’s linking to your entries is writing something related to your entry, and if the document http://example.com/related.html is doing this, you can add:

<link
  rev="related"
  href="http://example.com/related.html"
/>

I’m quite confident there are plenty more uses for reverse relationships than these two examples. Find them. Use them.