Computer Fundamentals : Pradeep K. Sinha& Priti Sinha

Transcription

1 Computer Fundamentals Pradeep K. Sinha Priti Sinha Chapter 18 The Internet Slide 1/23 Learning Objectives In this chapter you will learn about: Definition and history of the Internet Its basic services The World Wide Web (WWW) WWW browsers Internet search engines Uses of the Internet Slide 2/23 Definition and History Slide 3/23 1

2 Definition and History The Internet is a network of computers, which links many different types of computers all over the world It is a network of networks sharing a common mechanism for addressing computers, and a common set of communication protocols The Internet has its root in the ARPANET system of the Advanced Research Project Agency of the U.S. Department of Defense ARPANET was the first WAN and had only four sites in 1969 The Internet evolved from basic ideas of ARPANET for interconnecting computers (Continued on next slide) Ref. Page 383 Slide 4/23 Definition and History In 1989, the U.S. Government lifted restrictions on the use of the Internet, and allowed its usage for commercial purposes as well It now interconnects more than 30,000 networks, allowing more than 10 million computers, and more than 50 million computer users in more than 150 countries around the world to communicate with each other Ref. Page 383 Slide 5/23 Its Basic Services Slide 6/23 2

3 Basic Services of the Internet Electronic Mail ( ): Allows a user to send a mail (message) to another Internet user in any part of the world in a near-real-time manner File Transfer Protocol (FTP): Allows a user to move a file from one computer to another on the Internet Telnet: Allows a user to log in to another computer somewhere on the Internet Usenet News: Allows a group of users to exchange their views/ideas/information Ref. Page 383 Slide 7/23 Electronic Mail is a rapid and productive communication tool because: It is faster than paper mail Unlike telephone, the persons communicating with each other need not be available at the same time Unlike fax documents, documents can be stored in a computer and be easily edited using editing programs Ref. Page 384 Slide 8/23 File Transfer Protocol Moving a file from a remote computer to ones own computer is known asdownloading Moving a file from ones own computer to a remote computer is known asuploading Anonymousftpsite is a computer allowing a user to log in with a username of anonymous and password that is user s address. Anonymous ftp sites are called publicly accessible sites because they can be accessed by any user on the Internet Ref. Page 384 Slide 9/23 3

4 Telnet Some common uses of telnet service are: Using the computing power of the remote computer Using a software on the remote computer Accessing remote computer s database or archive Logging in to ones own computer from another computer Ref. Page 385 Slide 10/23 Usenet News Several usenet news groups exist on the Internet and are called newsgroups In a moderated newsgroup only selected members have the right to directly post (write) a message to the virtual notice board. Other members can only read the posted messages In a nonmoderated newsgroup any member can directly post a message to the virtual notice board A moderated newsgroup ensures quality of posted messages Netiquette (network etiquette) deals with rules of framing messages that will not hurt others Ref. Page 385 Slide 11/23 The World Wide Web (WWW) Slide 12/23 4

5 The World Wide Web (WWW) World Wide Web (WWW or W3) is the most popular and promising method of organizing and accessing information on the Internet Hypertext is a new way of information storage and retrieval that enables authors to structure information in novel ways A properly designed hypertext document can help users locate desired type of information rapidly Hypertext documents enable this by using a series of links A link is a special type of item in a hypertext document connecting the document to another document Hypertext documents on the Internet are known as Web Pages (Continued on next slide ) Ref. Page 386 Slide 13/23 The World Wide Web (WWW) Web page designers create Web Pages by using a special language called HyperText Markup Language (HTML) HTML is a subset of a more generalized language called Standard Generalized Markup Language (SGML) HTML is now a de-facto industrial standard for creating Web Pages The WWW uses client-server model, and an Internet Protocol called HyperText Transport Protocol (HTTP) Any computer on the Internet using the HTTP protocol is called a Web Server Any computer accessing that server is called a Web Client Ref. Page 386 Slide 14/23 Example of Hypertext Document Pradeep K. Sinha has been involved in the research and development of distributed systems for almost a decade. At present Dr. Sinha is working at the Centre for Development of Advanced Computing (C-DAC), Pune, India. Before joining C-DAC, Dr. Sinha worked with the Multimedia Systems Research Laboratory (MSRL) of Panasonic in Tokyo, Japan. Links Ref. Page 386 Slide 15/23 5

6 WWW Browsers To use a computer as a web client, a user needs to load on it a special software tool known aswwwbrowser(browser) Browsers provide following navigation facilities: Do not require a user to log in to a server computer Enable a user to visit a server computer s site directly and access information on it by specifying its URL (Uniform Resource Locator) Enable a user to create and maintain a personal hotlist of favorite URL Maintain a history of server computers visited by a user in a surfing session Enable a user to download information in various formats Ref. Page 387 Slide 16/23 Internet Search Engines Slide 17/23 Internet Search Engines Internet search engine is an application, which helps users locate web sites containing useful information and references To search information: A user types the description of the information using the user interface of the search engine The search engine then searches the requested information on the WWW and returns the results to the user Results enable the user to locate the requested information quickly from the vast ocean of information available on the Internet Slide 18/23 6

7 Major Elements of Internet Search Engines Search Request Interface Enables users to provide description of desired information to the search engine Search engine may allow specifications of simple keywords and phrases, combination of keywords and phrases using Boolean operators and exclusion/inclusion operators, and title and URL limiters Information Discoverer Discovers information from the WWW and creates a database for the search engine Search engine uses the database to locate useful information during the search process Information discoverer accrues this information in two-ways: In manual method, authors provide information about their websites (Continued on next slide ) Slide 19/23 Major Elements of Internet Search Engines In automatic method, information discoverer collects the information using programs, such as web crawlers, spiders, robots Presenter of Search Results Returns search results, ranking them in an order Search engines often list search results in accordance to a relevance score Relevance scores reflect the number of times a search term appears in a web page Some search engines also allow users to control relevance score by giving different weights Slide 20/23 Some Popular Internet Search Engines HotBot ( Yahoo ( Lycos ( Infoseek ( Google ( Inference Find ( Ixquick ( Slide 21/23 7

8 Uses of the Internet Some important current strategic uses of the Internet are: On-line communication Software sharing Exchange of views on topics of common interest Posting of information of general interest Organization promotion Product promotion and feedback about products Customer support service On-line journals, magazines, encyclopedia, and dictionary On-line shopping World-wide video conferencing World-wide web casting Slide 22/23 Keywords/Phrases Anonymous ftp site Browser Download Electronic mail ( ) File Transfer Protocol (FTP) Hypertext Hypertext Transport Protocol (HTTP) Internet Internet search engine Netiquette Newsgroup On-line shopping Publicly accessible sites Standard Generalized Markup Language (SGML) Telnet Uniform Resource Locator (URL) Upload Usenet Video conferencing Web casting Web client Web crawler Web Server World Wide Web (WWW) Slide 23/23 8