香港城市大学：Rank Aggregation in MetaSearch

Lecture 9: Rank Aggregation in Metasearch Meta Search Engine · socia/ Choice rules Rank Aggregation

Lecture 9: Rank Aggregation in MetaSearch • MetaSearch Engine • Social Choice Rules • Rank Aggregation

Choices of Search Engines Many search engines exist to compete for users The results are not necessarily the same Different users prefer different search engines Search results may, in the future, be biased towards paid advertisements

Choices of Search Engines • Many search engines exist to compete for users – The results are not necessarily the same – Different users prefer different search engines – Search results may, in the future, be biased towards paid advertisements

Meta Search Engine Metasearch engines are designed to increase the coverage of web by forwarding users' queries to multiple search engines Users requests are sent to multiple search engines such as alltheWeb google MSN Then the results from the individual search engine are combined into a single result set to present to users

MetaSearch Engine • Metasearch Engines are designed to increase the coverage of web by forwarding users’ queries to multiple search engines – Users’ requests are sent to multiple search engines such as AlltheWeb, Google, MSN. • Then the results from the individual search engine are combined into a single result set to present to users

Different forms of meta search Submit different representations of the same query to the same search engine, then combine the results Submit the same query to several search engine adopting different information retrieval models then combine the results

Different Forms of MetaSearch • Submit different representations of the same query to the same search engine, then combine the results. • Submit the same query to several search engine adopting different information retrieval models, then combine the results

Issues How to combine the results retrieved by different source search engines is crucial for the success of a metasearch engine And this is the problem that social choice theory has been trying to answer

• How to combine the results retrieved by different source search engines is crucial for the success of a metasearch engine. • And this is the problem that social choice theory has been trying to answer. Issues

Search Engine Watch Interesting meta search engines are listed at http://www.searchenginewatch.com/links/article.ph p/2156241

Search Engine Watch • Interesting meta search engines are listed at – http://www.searchenginewatch.com/links/article.ph p/2156241

Social Choice Theory Studies on protocols that help a group of people make collective decisions such as vote

Social Choice Theory • Studies on protocols that help a group of people make collective decisions, such as vote

A Fundamental problem Given a collection of agents(voters) with preferences over different alternatives (allocations, outcomes) how should society evaluate these alternatives and make a decision for all that may be for the will of some voters but against that of others

A Fundamental problem • Given a collection of agents (voters) – with preferences over different alternatives (allocations, outcomes), • how should society evaluate these alternatives and make a decision for all – that may be for the will of some voters but against that of others

Applications Voters elect president from several candidates National polls for economic or political policy of the government The procedure or rule of election The rank of metasearch engine obtained from those of search engines

Applications • Voters elect president from several candidates. • National polls for economic or political policy of the government • The procedure or rule of election • The rank of metasearch engine obtained from those of search engines

Group Descisions How do we make decisions Flip a coin? Dictatorship ? Democracy(Majority rule)?

Group Descisions How do we make decisions • Flip a coin? • Dictatorship? • Democracy (Majority rule)?