Transcript Document
The Internet Book 1 Chapter 25 Description Of Functionality • An automated search service allows one to find information that resides on remote computers. 3 Browsing Vs. Automated Searching • The size of the Internet makes it impossible to find specific information by searching one computer at a time. –Called Browsing • The solution is to use an automated search engine. 4 A Search Engine Helps Users Get Started • Automated searching is especially helpful when a user first begins to explore a topic. 5 A Search Tool Can Help Recover From Loss • Automated search tools help users recover quickly when the location of information is lost. 6 Automated Searching By Name • One can search by specific name or content. 7 How An Automated Search Service Operates • Search engines: –gather information –store it locally • Servers do not have to search the entire Internet when responding to a user’s request. 8 Figure 25.1 Figure 25.1 An illustration of the two-step process an automated search service uses. (a) A spider program automatically contacts web sites and obtains a list of available items. (b) When someone uses a browser to contact the search engine, the server consults the database on its local disk. Modern Systems Search Web Page Contents • Users can assume the search will look for Web pages matching the topic specified. 10 How A Web Search Appears To A User • Search services are: –Accessed through a Web site • Search services: –Require user interaction –Use forms technology 11 Figure 25.2 Figure 25.2 An illustration of how the Web page for a search service might appear. How A Search Engine Returns Results • The search engine creates a Web page that has a link to each found topic. –Uses cgi technology to create pages dynamically 13 Figure 25.3 Figure 25.3 Illustration of the main part of the user’s screen after a search engine returns the results of a search. Automated Search Services Use String Matching • The simplest automated search mechanism is string matching. • The user enters a topic, the search engine finds Web pages that contain that topic string. 15 String Matching • Advantages of string matching – Simplicity • Disadvantage of string matching – Lack of semantics – Inability to tell meaning of word 16 Advanced Search Programs • Some search engines offer multi-key search service. –Group synonyms with a common theme together 17 Advanced Services- More Sophisticated Matching • Some services offer the opportunity to give more detailed specifications. •Use plus sign to denote a required term 18 Personalized Search Results • Search engines keep information about users and use the information to select and order search results. –Results in users getting different search results 19 How An Automated Content Search Works • The search service runs a program called a spider. –Explores Web –Compiles a list of topics –Stores list on server disk • This is one way to avoid useless information. 20 Searches Are Restricted • Automated search services search only the beginning of each page. –Use the META tag: •Allows specific keywords that do not appear in the browser 21 Advertising Pays For Searching • Web searching appears to be free. –Uses advertising to generate revenue 22 Example of Automated Search Services Figure 25.4 Examples of automated search services available on the World Wide Web. Although most services provide a general index to Web pages, a few are restricted to specific types of information. Significance Of Automated Web Search • Automated search engines have become an essential part of finding information. –Growing rapidly on the Internet 24 Conclusion • How do search engines help users find information on the Web? 25 Glossary • Personalized Search Results – Results from a search engine that are personalized to the user who makes the request. Personalization depends on a history of searches and web accesses. 27 Glossary • Wide Area Information Server – (WAIS) An early automated search service tht permitted one to locate documents that contain key words or phrases. 28