Relevance Using Hyperlinks (Cont.) Solution:use number of hyperlinks to a site as a measure of the popularity or prestige of the site Count only one hyperlink from each site (why?-see previous slide) Popularity measure is for site,not for individual page But,most hyperlinks are to root of site Also,concept of"site"difficult to define since a URL prefix like cs.yale.edu contains many unrelated pages of varying popularity ■Refinements When computing prestige based on links to a site,give more weight to links from sites that themselves have higher prestige Definition is circular Set up and solve system of simultaneous linear equations Above idea is basis of the Google PageRank ranking mechanism Database System Concepts-7th Edition 31.10 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 31.10 ©Silberschatz, Korth and Sudarshan th Edition Relevance Using Hyperlinks (Cont.) ▪ Solution: use number of hyperlinks to a site as a measure of the popularity or prestige of the site • Count only one hyperlink from each site (why? - see previous slide) • Popularity measure is for site, not for individual page ▪ But, most hyperlinks are to root of site ▪ Also, concept of “site” difficult to define since a URL prefix like cs.yale.edu contains many unrelated pages of varying popularity ▪ Refinements • When computing prestige based on links to a site, give more weight to links from sites that themselves have higher prestige ▪ Definition is circular ▪ Set up and solve system of simultaneous linear equations • Above idea is basis of the Google PageRank ranking mechanism