The idea of doing link analysis to compute a popularity rank is older than PageRank. Other variants of the same idea are currently in use – grade schoolers do the same sort of computations in picking kickball teams. But in all seriousness, these ideas can be categorized into three main categories: rank of individual pages and nature of web site content. Search engines often differentiate between internal links and external links, because web masters and mistresses are not strangers to shameless self-promotion. Link map data structures typically store the anchor text embedded in the links as well, because anchor text can often provide a “very good quality” summary of a web page's content.