Relevance Using Hyperlinks Number of documents relevant to a query can be enormous if only term frequencies are taken into account ■Using term frequencies makes“spamming”easy E.g.,a travel agency can add many occurrences of the words "travel"to its page to make its rank very high Most of the time people are looking for pages from popular sites Idea:use popularity of Web site (e.g.,how many people visit it)to rank site pages that match given keywords Problem:hard to find actual popularity of site ·Solution:next slide Database System Concepts-7th Edition 31.9 ©Silberscha乜，Korth and SudarshanDatabase System Concepts - 7 31.9 ©Silberschatz, Korth and Sudarshan th Edition Relevance Using Hyperlinks ▪ Number of documents relevant to a query can be enormous if only term frequencies are taken into account ▪ Using term frequencies makes “spamming” easy ▪ E.g., a travel agency can add many occurrences of the words “travel” to its page to make its rank very high ▪ Most of the time people are looking for pages from popular sites ▪ Idea: use popularity of Web site (e.g., how many people visit it) to rank site pages that match given keywords ▪ Problem: hard to find actual popularity of site • Solution: next slide