searchengines - Fall 2006 Davison/Lin CSE 197/BIS 197:...

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Unformatted text preview: Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-1 How Search Engines Work Today we show how a search engine works What happens when a searcher enters keywords What was performed well in advance Also explain (briefly) how paid results are chosen If we have time, we will also talk about the size of the Web (If you really want to know how web search engines work, take my CSE345 WWW Search Engines course in the spring!) Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-2 (Google results example) ORGANIC RESULTS PAID RESULTS Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-3 Building an index A search engine does not examine every page on the web when a user puts in a query The engine first builds an index Custom database of all the words on all pages Search engine also stores other information Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-4 Overview of organic search Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-5 Matching the Search Query The search query is everything that the user types to get results It is made up of one or more search terms , plus optional special characters Analyzing the Query Expanding the query Word variants: plural/singular, various verb forms Spelling correction Phrases, anti-phrases, and stop words Word order Search operators Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-6 Matching the Search Query Organic query matches Find pages with each of the remaining query terms Document IDs are listed in a term index Document information is in a separate doc index Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-7 Matching the Search Query Paid placement matches Similar to organic match, but using a separate database of ads Uses similar processing to select which query terms to use Advertisers choose which queries can match Might require exact match, or allow broad matching Simpler/faster because there are fewer ads to search through Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-8 Ranking Organic Matches This is a complex, active research area Goal is to sort matching results from 'best' to 'worst' Many factors contribute to different rankings in the various engines Ranking functions are under continuous change Primary factors Text analysis: keyword density and prominence Link analysis: page and site authority estimates Anchor text: terms used to describe page by others Traffic analysis: which results get clicked on Fall 2006 Davison/Lin CSE 197/BIS 197: Search Engine Strategies 2-9 Text Analysis: Keyword Density A.k.a. keyword weight Generally refers to the relative frequency of a term on the page Higher keyword density generally means that a document is more 'about' that keyword Natural text has a maximum reasonable density...
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This note was uploaded on 08/06/2008 for the course CSE 197 taught by Professor Hectormunoz-avila during the Fall '07 term at Lehigh University .

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searchengines - Fall 2006 Davison/Lin CSE 197/BIS 197:...

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