XFN is a neglected microformat protocol for adding meaning to links between people (and their blogs or home pages). It just requires the use of some specific keywords in the rel attribute of the a tag that describes your relationship to the person at the linked site.
<a href="http://somewhere.com" rel="friend met">Phil</a>I have introduced this while teaching basic HTML, asking students to add links to three or four of their colleagues homepages.
The nice thing about this is that you can then use a specialised web spider such as [XFNGraph][xg] to crawl the friends network and visualise it. The tool recognises the different types of relationship and codes the edges accordingly (solid if met, blue if friend etc..)
This provides great opportunities to explain the web as a directed graph, implementing an asymmetric “follows” pattern. It becomes possible to see who is popular and influential in the network and to illustrate the importance of being linked up.
XFN: http://gmpg.org/xfn/
[xg]: http://xfngraph.sourceforge.net/index.en.utf8.html XFN Graph : http://xfngraph.sourceforge.net/index.en.utf8.html
**Update: Here’s a basic XFN spider example using JavaScript and visjs.