Saturday, August 05, 2006

Outbound links PageRank Calculation

Outbound links are a drain on a site's total PageRank. They leak PageRank. To counter the drain, try to ensure that the links are reciprocated. Because of the PageRank of the pages at each end of an external link, and the number of links out from those pages, reciprocal links can gain or lose PageRank. You need to take care when choosing where to exchange links.

When PageRank leaks from a site via a link to another site, all the pages in the internal link structure are affected. (This doesn't always show after just 1 iteration). The page that you link out from makes a difference to which pages suffer the most loss. Without a program to perform the calculations on specific link structures, it is difficult to decide on the right page to link out from, but the generalization is to link from the one with the lowest PageRank.

Many websites need to contain some outbound links that are nothing to do with PageRank. Unfortunately, all 'normal' outbound links leak PageRank. But there are 'abnormal' ways of linking to other sites that don't result in leaks. PageRank is leaked when Google recognizes a link to another site. The answer is to use links that Google doesn't recognize or count. These include form actions and links contained in javascript code.

Form actions
A form's 'action' attribute does not need to be the url of a form parsing script. It can point to any html page on any site. Try it.

Example:
form_name="myform" action="http://www.domain.com/somepage.html">
a href="javascript:document.myform.submit()">Click here (/a>


To be really sneaky, the action attribute could be in some javascript code rather than in the form tag, and the javascript code could be loaded from a 'js' file stored in a directory that is barred to Google's spider by the robots.txt file.

Javascript
Example:
a href="javascript:goto('wherever')">Click here (/a>

Like the form action, it is sneaky to load the javascript code, which contains the urls, from a seperate 'js' file, and sneakier still if the file is stored in a directory that is barred to googlebot by the robots.txt file.

The "rel" attribute
As of 18th January 2005, Google, together with other search engines, is recognising a new attribute to the anchor tag. The attribute is "rel", and it is used as follows:-

a href="http://www.domain.com/somepage.html" rel="nofollow">link text (/a>

The attribute tells Google to ignore the link completely. The link won't help the target page's PageRank, and it won't help its rankings. It is as though the link doesn't exist. With this attribute, there is no longer any need for javascript, forms, or any other method of hiding links from Google.

1 comment:

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