Web Search Overview Crawling IR Big Issues in IR Relevance Retrieval models define a view of relevance Ranking algorithms used in search engines are based on retrieval models Most models describe statistical properties of text rather than linguistic i.e., counting simple text features such as words instead of parsing and analyzing the sentences Statistical approach to text processing started with Luhn in the 50s Linguistic features can be part of statistical model 14Web Search Overview & Crawling 14 Big Issues in IR ▪ Relevance ▪ Retrieval models define a view of relevance ▪ Ranking algorithms used in search engines are based on retrieval models ▪ Most models describe statistical properties of text rather than linguistic ▪ i.e., counting simple text features such as words instead of parsing and analyzing the sentences ▪ Statistical approach to text processing started with Luhn in the 50s ▪ Linguistic features can be part of a statistical model IR