Search Engines SCI199


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Search Engines SCI199

  1. 1. Search Engines SCI199 Oct. 5, 2009 Phillipa Gill [email_address]
  2. 2. How do search engines work? Meta-Tags <ul><li><html> </li></ul><ul><li><head> </li></ul><ul><li>#meta tags go here </li></ul><ul><li></head> </li></ul><ul><li><body> </li></ul><ul><li></body> </li></ul><ul><li></html> </li></ul><ul><li>Example meta tags: </li></ul><ul><li><meta http-equiv=“Content-Type” content=“text/html”> </li></ul><ul><li><meta name=“zipcode” content=“11021,11208,11234”> </li></ul>
  3. 3. How do search engines work? Meta-Tags <ul><li>Keywords meta-tag (most relevant for search) </li></ul><ul><li>Example: </li></ul><ul><li><meta name=“keywords” content=“encyclopedia, wikipedia”> </li></ul><ul><li>Name that site: (tags with site name removed  ) </li></ul><ul><li>1. <meta name=&quot;keywords&quot; content=&quot;video, sharing, camera phone, video phone, free, upload&quot;> </li></ul><ul><li>2. <meta name=&quot;keywords&quot; content=&quot;Co-operative, Mathematics, Science, Arts, Health, Engineering, Higher, education, Ontario, Canada, co-op.&quot; /> </li></ul><ul><li>3. <meta name=&quot;keywords&quot; content=&quot;Books, Online Shopping, Book Store, Music, Canadian Music, CDs, DVDs, Videos, Electronics, Cameras, Media Players, Video Games, Computers, Software&quot; /> </li></ul>
  4. 4. How do search engines work? Meta-Tags <ul><li>If you were building a site and wanted to be ranked highly in Google what might you try? </li></ul><ul><li>E.g., Pretend you are Ford with a site about your F150 truck, what keywords might you include? </li></ul><ul><li>Consequence: Keywords not highly used any more. </li></ul>
  5. 5. How do search engines work? Page Rank <ul><li>Use links to rank results (simplified example) </li></ul>A B C D 0.25 0.25 0.25 0.25 <ul><li>Everyone gets page rank that is 1/(number of pages) = ¼ </li></ul><ul><li>Each page gets it’s page rank updated based on incoming links. </li></ul><ul><li>In this case page rank of A PR(A) is: </li></ul><ul><li>PR(A) = 0.25 + 0.25 + 0.25 = 0.75 </li></ul>0.25 0.25 0.25
  6. 6. How do search engines work? Page Rank <ul><li>Links are weighted based on number of outgoing links </li></ul>A B C D 0.25 0.25 0.25 0.25 0.25/1 0.25/3 0.25/2 0.25/3 0.25/3 0.25/2 The page rank is divided by the number of outgoing links a site has (why?) e.g., D’s links are worth 0.25/3 because it has 3 outgoing links now: PR(A)=0.25/2 + 0.25/1 + 0.25/3
  7. 7. Search Engine Optimization <ul><li>Attempting to optimize Web sites so they can be found easily by search engines </li></ul><ul><ul><li>Requires knowledge of the search engine algorithms </li></ul></ul><ul><li>Can use legitimate means </li></ul><ul><ul><li>e.g., changing HTML to be more search engine friendly </li></ul></ul><ul><li>Can also use unethical means </li></ul><ul><ul><li>Link farms, keyword stuffing etc. </li></ul></ul>
  8. 8. How do you evaluate search engine results? <ul><li>Demo/Discussion </li></ul>