1. Search Engines SCI199 Oct. 5, 2009 Phillipa Gill phillipa@cs.toronto.edu

2. How do search engines work? Meta-Tags #meta tags go here Example meta tags:

3. How do search engines work? Meta-Tags Keywords meta-tag (most relevant for search) Example: Name that site: (tags with site name removed ) 1. 2. 3.

4. How do search engines work? Meta-Tags If you were building a site and wanted to be ranked highly in Google what might you try? E.g., Pretend you are Ford with a site about your F150 truck, what keywords might you include? Consequence: Keywords not highly used any more.

5. How do search engines work? Page Rank Use links to rank results (simplified example) AB CD 0.25 1.Everyone gets page rank that is 1/(number of pages) = ¼ 2.Each page gets it’s page rank updated based on incoming links. In this case page rank of A PR(A) is: PR(A) = 0.25 + 0.25 + 0.25 = 0.75 0.25

6. How do search engines work? Page Rank Links are weighted based on number of outgoing links AB CD 0.25 0.25/1 0.25/3 0.25/2 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. Search Engine Optimization Attempting to optimize Web sites so they can be found easily by search engines –Requires knowledge of the search engine algorithms Can use legitimate means –e.g., changing HTML to be more search engine friendly Can also use unethical means –Link farms, keyword stuffing etc.

8. How do you evaluate search engine results? Demo/Discussion