Search Engines: The players and the field The mechanics of a typical search. The search engine wars. Statistics from search engine logs. The architecture of a search engine. The query engine.

Mechanics of a typical search

Results & ads returned ranked

Category of first result

Result for phrase query

Search on the Web Corpus: The publicly accessible Web: static + dynamic Goal: Retrieve high quality results relevant to the user’s need (not docs!) Need Informational – want to learn about something Navigational – want to go to that page Transactional – want to do something (web-mediated)  Access a service  Downloads  Shop Gray areas  Find a good hub  Exploratory search “see what’s there” Low hemoglobin United Airlines Tampere weather Mars surface images Nikon CoolPix Car rental Finland Abortion morality

Search Engines as Info Gatekeepers Search engines are becoming the primary entry point for discovering web pages. Ranking of web pages influences which pages users will view. Exclusion of a site from search engines will cut off the site from its intended audience. The privacy policy of a search engine is important. Introna & Nissenbaum: Defining the Web: The Politics of Search Engines Hindman et al: Googlearchy: How a few Heavily-Linked Sites Dominate Politics on the Web

Search Engine Wars The battle for domination of the web search space is heating up! The competition is good news for users! Crucial: advertising is combined with search results! What if one of the search engines will manage to dominate the space?

Yahoo! Synonymous with the dot-com boom, probably the best known brand on the web. Started off as a web directory service in 1994, acquired leading search engine technology in Has very strong advertising and e-commerce partners

Lycos! One of the pioneers of the field Introduced innovations that inspired the creation of Google

Google Verb “google” has become synonymous with searching for information on the web. Has raised the bar on search quality Has been the most popular search engine in the last few years. Had a very successful IPO in August Is innovative and dynamic. Has restored glamour in CS lost in dot-com-bust

Live Search ( was: MSN Search) Synonymous with PC software. Remember its victory in the browser wars with Netscape. Developed its own search engine technology only recently, officially launched in Feb May link web search into its next version of Windows.

Ask Jeeves Specialises in natural language question answering. Search driven by Teoma.Teoma

Cuil The latest kid on the block Claims to have indexed 120B pages! So far, it does not rank!

Experiment with query syntax Default is AND, e.g. “computer chess” normally interpreted as “computer AND chess”, i.e. both keywords must be present in all hits. “+chess” in a query means the user insists that “chess” be present in all hits. “computer OR chess” means either keywords must be present in all hits. “”computer chess”” means that the phrase “computer chess” must be present in all hits.

Statistics from search engine logs Statistic (Year) AltaVista (1998) AlltheWeb (2002) Excite (2001) average terms per query average queries per session average result pages viewed usage of advanced search features 20.4%1.0%10.0%

The most popular search keywords AltaVista (1998)AlltheWeb (2002)Excite (2001) sexfree appletsex pornodownloadpictures mp3softwarenew chatuknude

Web search Users Ill-defined queries Short length Imprecise terms Sub-optimal syntax (80% queries without operator) Low effort in defining queries Wide variance in Needs Expectations Knowledge Bandwidth Specific behavior 85% look over one result screen only mostly above the fold 78% of queries are not modified  1 query/session Follow links – “the scent of information”...

Query Distribution Power law: few popular broad queries, many rare specific queries

How far do people look for results? (Source: iprospect.com WhitePaper_2006_SearchEngineUserBehavior.pdf)iprospect.com

Architecture of a Search Engine The Web Ad indexes Web spider Indexer Indexes Search User

Rate of web content change 720K pages from 270 popular sites sampled daily from Feb 17 – Jun 14, 1999 [Cho00] Mathematically, what does this seem to be? What does this suggest for crawling policy?

Diversity Languages/Encodings Hundreds of languages, W3C encodings: 55 (Jul01) [W3C01] Home pages (1997): English 82%, Next 15: 13% [Babe97] Google (mid 2001): English: 53%, JGCFSKRIP: 30% Document & query topic Popular Query Topics (from 1 million Google queries, Apr 2000) 1.8%Regional: Europe7.2%Business ………… 2.3%Business: Industries7.3%Recreation 3.2%Computers: Internet8%Adult 3.4%Computers: Software8.7%Society 4.4%Adult: Image Galleries10.3%Regional 5.3%Regional: North America13.8%Computers 6.1%Arts: Music14.6%Arts

Search Index - Inverted File Also store position of word in web page (“offset”) and information on HTML structure. Frequency

The query engine The interface between the search index, the user and the web. Algorithmic details of commercial search engines are kept as trade secrets. First step is retrieval of potential results from the index. Second step is the ranking of the results based on their “relevance” to the query.

Portal User Interface

Crawling the Web Mode of crawl: BFS Frequency of crawl: important robots.txt gives explicit directions on what not to crawl Parallel machines crawl all the time