1. Search Engines

2. Allows a user to find information residing on remote computers; Searching differs from browsing in that the user is not required to provide a URL; Search engines are programs that search Web pages related to a given topic like: Company Individual Product Brand Results of the search are returned as a Web page; Q. What type of page is returned?

3. Search Engines (cont.) Provide users a starting point in their search Especially useful considering the size of the WWW Can automatically recover the location of an item after a loss caused by power outage, say. Two types of search engines: Search by name; Search by content.

4. Automated Searching by Name Respond to questions of the form: “among the files on the WWW, where are the files that have name x?” Similar to “Find” program on PCs. Ex: archie

5. Automated Searching by Content Most (if not all) current search engine search the content; To make a search a user has to: Download the page of the search engine; Enter the topic; Send the requested topic to the server; The server processes the request and sends back the matching pages. Ex. www.google.com Q. What type of page is needed for the main page of the server? What type of page is needed for the result?

6. How a Search Engine Operates Naïve approach: search the WWW when a request arrives: Takes too long Instead: Before the search engine becomes operational a list of available information on the WWW is compiled, sorted, indexed, and stored on a local disk; To deal with changes, computer programs called spiders or crawlers that probe the WWW continuously and report new pages to the server

7. How a Search Engine Operates (cont.) String matching is used to find documents related to a given topic; Advantages: Simplicity Efficient Disadvantage: Lack of semantic Ex: a search for “automobile” will not return documents containing “car”.

8. Performance Issues Two types of performance issues: the relevance of the result pages; The time taken to perform a search; To improve the relevance of the result a user may: enter several terms: Ex: car vehicle automobile Specify which words are required: Ex. consider that a plus sign denote a required term, then a user might request “+rock +music” Use quotes Ex: “The Postman Always Rings Twice”

9. Performance Issues (cont.) To speed up search the search engine looks only at the beginning of the page;