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Siena CSIS 116 - Searching on the WWW The Google Phenomena

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Searching on the WWW The Google PhenomenaSearchingPowerPoint PresentationSlide 4Organizing InformationProblem With HierarchiesWebs or NetworksProblem With Web NetworksSlide 9Search Engines to the RescueHow Search Engines WorkSlide 12Step 1: Web CrawlingStep 2: Web IndexingSlide 15Step 3: User SearchStep 4: Ranking the resultsSearch Engine IssuesSearch Engines (Catch 22)How Google became the bestPageRank continuedPageRank intuitionSlide 23Searching on the WWWThe Google PhenomenaSnyder p119-141SearchingThe best place to look for something is where it’s likely to be foundKey to finding information.SearchingA lot of information can be found on the WWWBut, that is the flaw of the WWW:Too much InformationNo organizationNo structureOrganizing InformationClassificationHierarchyCategories with sub-categoriesWhat are some problems with Hierarchies?Problem With HierarchiesI want to find the requirements for the Minor in ISSiena CollegeAcademics Financial Aid AthleticsDegree RequirementsFormsSchoolsScienceCSArtsIS MinorWebs or NetworksMultiple PathsSiena CollegeAcademics Financial Aid AthleticsDegree RequirementsFormsSchoolsScienceCSArtsIS MinorProblem With Web NetworksLess Important to Get things in the correct categoryInformation architects don’t worry too much aboutClassificationOrganizationProblem With Web NetworksAs different Networks of Information are connectedExcessive redundant links emergeDifferent organization strategies classA mess is createdSearch Engines to the RescueAlternative to searching via navigationhttp://www.marketwatch.com/newsimages/misc/search_engines_timeline.pdfHow Search Engines Work1. Web Crawling – program (robot) surfs from hyper-link to hyper-link accumulating pages2. Web Indexed – each accumulated page is added to a database.URL of web page is storedEach word, occurrences, and sometimes position are stored.How Search Engines Work3. User Search – actually searches the index database4. Sophisticated Algorithms are used to retrieve and rank pages that “match” the user search.Step 1: Web CrawlingHardest task.5 - 10 million new web pages are added to the Internet every day.Robots need to know where to start lookingYou need the help and cooperation of web page creators.Step 2: Web IndexingEach URL consists of a list of words...URL1  word5  word74  word195  word456URL2  word7  word82  word135URL3  word5  word74  word165  word288URL4  word21  word59 URL5  word25  word74  word188  word432URL6  word7  word186  word430URL7  word2  word398 URL8  word34  word39  word84  word193...Step 2: Web IndexingInverted Index: Each word consists of a list of URLsword1  URL19  URL39  URL82  URL91word2  URL27  URL41  URL66  URL67word3  URL49  URL75  URL65word4  URL29  URL89word5  URL12  URL48  URL66word6  URL53  URL73  URL123  URL144word7  URL3  URL41  URL77...Step 3: User SearchSearching the index database must be quick.The database is sorted by key words (primary index)The English language has about 600,000 wordsLuckily, only about a tenth them are widely usedThe database server needs to store the primary index in memory (RAM).Step 4: Ranking the results Searches on common words can return millions of pages.Ordering or ranking becomes more important as the data increasesIntuitive measuresNumber of occurances of search wordsSearch word in title, keyword, etc“Importance” of web pageUser feedback.Search Engine IssuesLogical statements AND, OR, etc.Phrases “Grilled Cheese”Images – Dali ExampleDishonesty – XXX ExampleDifferences in Vocabulary - IBM-IssueSearch Engines (Catch 22)Search Engine Companies make money by placing ads.More searches = bigger audience = more $$$ from adsBest Thing: Get as many people to use your search engine as possibleWorst Thing: What if everyone exclusively uses search engines to search the WWW?How Google became the bestPageRank algorithm (based on the Clever Algorithm)PageRank is a measure of importance.Links from important pages improves your PageRank1.2 1.62.4 3.1 2.0 4.63.812.1PageRank continuedhttp://www.iprcom.com/papers/pagerank/Simplistic Explanation:Initially all pages have the same PageRankAn iterative process increases the page rank of all pages based on direct links first (highly weighted *1)then, one hop linksthen, two hop links... then, ten hop links (very low weighting *0.001)...The algorithm ignores cyclesThe algorithm does not reward cliquesEventually, the page ranks will stabilize (stop increasing) once you’ve considered Until the page ranks stablizePageRank intuitionESPN.com is highly ranked becauseSeveral other highly ranked pages point to itMillions of low ranked pages point to itAny page connected-to or part-of ESPN.com will benefit from this.Intuitively, ESPN is an information authority on sports.PageRank intuitionBreimer.net is poorly ranked becauseVery few pages point to it. None to be exact.The page is not an authority on “Breimer” until other pages acknowledge its existence via a


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