Today, Google made public it’s Social Graph API which is a way for web applications to consume specially tagged content that is designated as public connections. Google states they index the XHTML Friends Network (XFN), Friend of a Friend (FOAF) and other publicly declared connections.

What is XFN

XFN is a method that personifies web links. You are added in human element to a your links. This is possible by adding simple tags to the “rel” attribute of the anchor (<a>) tag. When you link out to other people or sites, you can designate your relationship to them. For example, if I was to link to my friend Joe, I would tag the link as follows:

Once you tag your appropriate links with XFN tags and others tag accordingly, you can build a plotted chart that depicts the relations between each of the members. Google’s My Connections application is a simple demonstration of how you can see how people are linked together.

XFN Tagging in WordPress

A popular place to tag your content with XFN is on your blog. If you are using WordPress as a blogging platform, then you can tag you blogroll links with the proper XFN tags. When you add a link, expand the “Link Relationship (XFN)” section beneathe the “Add Link” button. Simply select the appropriate tags and they will populate in the “rel” field.

Tagging your blogroll with the appropriate XFN and FOAF may result in an increase of traffic from the advent of communities and sites that will use the Google API and other methods of consuming XFN-tagged content.