（中职）计算机专业英语unit 6教学课件

1、YCF正版可修改PPT（中职）计算机专业英语unit 6教学课件 Unit 6 Internet and Its Applications 6. 1 Overview of Internet 6. 2 Internet Technology 6. 3 Search Tools 6. 4 E-mail6. 5 Distance Education 6. 6 Electronic Commerce wordPhrasesGrammarReference Translation In the general sense, an Internet ( with a lowercase “, ”a sh

2、ortened form of the original Internetwork ) is a computer network that connects several networks. As a proper noun, the Internet is the publicly available internationally interconnected system of computers ( plus the information and services they provide to their users ) that uses the TCP/IP suite o

3、f packet switching communications protocols. Thus, the largest Internet is called simply the Internet. The art of connecting networks in this way is called Internetworking. 6. 1. 1 The Creation of the InternetThe core networks forming the Internet started out in 1969 as the ARPANET devised by the Un

4、ited States Department of Defense Advanced Research Projects Agency ( ARPA ) . Some early research which contributed to ARPANET included work on decentralized networks，queuing theory and packet switching. On January 1, 1983，the ARPANET changed its core networking protocols from NCP to the then-new T

5、CP/IP, marking the start of the Internet as we know it today. 6. 1 Overview of Internet下一页返回Another important step in the development was the National Science Foundations ( NSF ) building of a university backbone, the NSFNET, in 1986. Important disparate networks that have successfully been accommod

6、ated within the Internet include Usenet, Fido net, and Bitnet. During the 1990s, the Internet successfully accommodated the majority of previously existing computer networks. This growth is often attributed to the lack of central administration, which allows organic growth of the network, as well as

7、 the non-proprietary nature of the Internet protocols, which encourages vendor interoperability and prevents one company from exerting control over the network. 6. 1. 2 Todays InternetEarly Internet pioneers-mostly educators and scientists-used primitive command line user interfaces to send E-mail,

8、transfer files and run scientific calculations on Internet supercomputers. Today, the Internet connects computers all over the globe and supplies information to people of all ages and interests. You can find job, communicate with customers, work out technical problems, sell products and conduct rese

9、arch.6. 1 Overview of Internet上一页下一页返回The primary use of the Internet is E-mail. Millions of people use the Internet for E-mail capabilities. E-mail, however, is only a small part of what the Internet offers. There is also chat groups, the World Wide Web, E-mail and mailing lists, bulletin boards an

10、d newsgroups, remote computer, file transfer. Users can join any of the thousands of Internet discussion groups, search for specific information in vast libraries, or transfer a variety of files to their computer. They can also explore the World Wide Web the Internets multimedia service. Over just t

11、he last few years Internet based resources and services have grown exponentially. Based on current productions this rapid growth will continue into the next decade as more businesses and consumers make the decision to move onto the Internet. 6. 1 Overview of Internet上一页返回To understand how you can us

12、e the Internet to access information from a computer that is located thousands of miles away, it is helpful to have a little background on the Internet communication network. Also you have to know the meanings of some terminologies, such as ISP, URL, browser, hypertext, home page, etc. 6. 2. 1 How D

13、oes Data Travel over the Internet?The cables, wires and satellites that carry Internet data form an interlinked communication network. Data travelling from one Internet host to another is transmitted from one link in the network to another, along the best possible route. If some links are overloaded

14、 or temporarily out of service, the data can be routed through different links. The major Internet communication links are called the Internet backbone. The efficient flow of data over the many communication links on the Internet requires a standard mechanism for routing data to its destination. TCP

15、/IP is the acronym for transforming control protocol/Internet protocol, a standard set of communication rules used by every computer that connects to the Internet. 6. 2 Internet Technology下一页返回TCP/IP knits together the Internet and allows data to travel smoothly over communication links provided by

16、NSPs worldwide. 6. 2. 2 Internet Service ProviderWhen you connect your computer to the Internet, you dont connect directly to the backbone. Instead, you connect it to an ISP that in turn connects to the backbone. An ISP is a company that maintains an Internet host computer providing Internet access

17、to businesses, organizations and individuals. An ISP works in much the same way as your local telephone company. You arrange for service-in this case for Internet access-and the ISP charges you a monthly fee. An ISP typically provides you with a user account that includes Internet access and an E-ma

18、il box. A connection that uses a phone line to establish a temporary Internet connection is referred to as a dial-up connection. Your computer dials your ISPs computer and establishes a connection using a phone line. Once you are connected, the ISPll route data between your computer and the Internet

19、 backbone. 6. 2 Internet Technology上一页下一页返回6. 2. 3 Internet Address and DomainThe Internet includes computers that perform different functions. Some computers on the Internet handle communications and route E-mail；others provide information. Regardless of its function, every computer that connects t

20、o the Internet has a unique identifying number called an IP address. An IP address is a set of four numbers between 0 and 255 that are separated by 4 dots. When data travels over the Internet, they carry the IP address of its destination. At each intersection on the backbone, a device called a route

21、r examines the datas IP address and then forwards the data towards its destination. Although an IP address works for inter-computer communications, people find it difficult to remember long strings of numbers. Therefore, many host computers also have an easy-to-remember name such as coca cola. com.

22、Most people refer to it as a domain name. A domain name ends with a three-letter extension that indicates its top-level domain. 6. 2 Internet Technology上一页下一页返回For example, in the domain name Coca-Cola. com, com indicates that the computer is maintained by a commercial business. A top-level domain g

23、roups the computers on the Internet into the categories shown in table 6-1.To understand how you can use the Internet to access information from a computer that is located thousands of miles away, it is helpful to have a little background on the Internet communication network. Also you have to know

24、the meanings of some terminologies such as ISP, URL, etc. 6. 2. 4 URLA web site is composed of a series of web pages that contain information. Each page is stored as a separate file and referred to by a unique URL. Like a domain name, a URL is an Internet address. A URL, however, is the address of a

25、 document on a computer, whereas a domain name represents the IP address of a computer. The components of a URL include the Web protocol, the Web server name, the folder in which the page is stored and the filename of the page. 6. 2 Internet Technology上一页下一页返回Web page URLs begin with http: /. The ac

26、ronym HTTP stands for Hypertext Transfer Protocol-the protocol, or communication system, that allows Web browsers to communicate with Web servers. Many of todays Web browsers assume that all Web addresses begin with http: /. If you are using such a browse, you can omit http: /when you type a URL. Th

27、e next part of the URL is the Web server name. A Web server is a computer that uses special software to transmit Web pages over the Internet. Many Web server names are domain names prefixed with www. Suppose you indicate to your browser that you want to access www. Google. com, by entering the Web s

28、erver name, you will access the sites home page. A home page is similar to the title page in a book. It identifies the site and contains links to other pages at the site. 6. 2 Internet Technology上一页下一页返回6. 2. 5 BrowserA browser is an application program that provides a way to look at and interact wi

29、th all the information on the World Wide Web. The word “browser” seems to have originated prior to the Internet as a generic term for user interfaces that let you browse ( navigate through and read ) text files on line. Technically, an Internet browser is a client program that uses HTTP ( Hypertext

30、Transfer Protocol ) to make requests of servers throughout the Internet on behalf of the browser user. Most browsers support E-mail and the File Transfer Protocol ( FTP ) but a Web browser is not required for those Internet protocols and more specialized client programs are more popular. The first W

31、eb browser, called World Wide Web, was created in 1990. That browsers name was changed to Nexus to avoid confusion with the developing information space known as the World Wide Web. The first Web browser with a graphical user interface was Mosaic, which appeared in 1993. 6. 2 Internet Technology上一页下

32、一页返回Many of the user interface features in Mosaic went into Netscape Navigator. Microsoft followed with its Internet Explorer ( IE ) . As of September 2006, Internet Explorer is the most commonly used browser, having won the so-called browser wars between IE and Navigator. Other browsers include: （1

33、）Firefox, which was developed from Mozilla ( the open source version of Navigator ) . （2）Flock, an open source browser based on Firefox and optimized for Web 2. 0 features such as blogging and social bookmarking. （3）Safari, a browser for Apple computers. （4）Lynx, a text-only browser for UNIX shell a

34、nd VMS users. （5）Opera, a fast and stable browser thats compatible with most relatively operating systems. 6. 2 Internet Technology上一页下一页返回6. 2. 6 HypertextHypertext is the organization of information units into connected associations that a user can choose to make. An instance of such an associatio

35、n is called a link or hypertext link. Hypertext was the main concept that led to the invention of the World Wide Web, which is nothing more ( or less ) than an enormous amount of information contents connected by an enormous number of hypertext links. 6. 2. 7 Home PageFor a Web user, the home page i

36、s the first Web page that is displayed after starting a Web browser like Netscapes Navigator or Microsofts Internet Explorer. The browser is usually preset so that the home page is the first page of the browser manufacturer. However, you can set it to open to any Web site. For example, you can speci

37、fy that “http: /www. yahoo. com ” or “http: /www. what is. com ” be your home page. 6. 2 Internet Technology上一页下一页返回You can also specify that there be no home page ( a blank space will be displayed ) in which case you choose the first page from your bookmark list or enter a Web address. For a Web si

38、te developer, a home page is the first page presented when a user selects a site or presence on the World Wide Web. The usual address for a Web site is the home page address, although you can enter the address ( Uniform Resource Locator ) of any page and have that page sent to you. 6. 2 Internet Tec

39、hnology上一页返回 The Web can be an incredible resource providing information on nearly any topic imaginable. Are you planning a trip? Writing an economics paper? Looking for a movie review? Trying to locate a long-lost friend? Information sources related to these questions, and much, much more are avail

40、able on the Web. With over two billion pages and more being added daily, the Web is a massive collection of interrelated pages. With so much available information, locating the precise information you need can be difficult. Fortunately, a number of organizations called search services or search prov

41、iders can help you locate the information you need. They maintain huge databases relating to information provided on the Web and the Internet. The information stored at these databases includes addresses, content descriptions or classifications, and keywords appearing on Web pages and other Internet

42、 informational resources. Special programs called agents, spiders, or bots continually look for new information and update the search services databases. 6. 3 Search Tools下一页返回Additionally, search services provide special programs called search engines that you can use to locate specific information

43、 of the Web. 6. 3. 1 Search EnginesSearch engines are specialized programs that assist you in locating information on the Web and the Internet. 1To find information, you go to the search services Web site and use their search engine. Yahoos search engine, like most others, provides two different sea

44、rch approaches. 1.Keyword SearchIn a keyword search, you enter a keyword or phrase reflecting the information you want. The search engine compares your entry against its database and returns a list of hits or sites that contain the keywords. Each hit includes a hyperlink to the referenced Web page (

45、 or other resource ) along with a brief discussion of the information contained at that location. Many searches result in a large number of hits. For example, if you were to enter the keyword travel, you would get over a thousand hits. 6. 3 Search Tools上一页下一页返回Search engines order the hits according

46、 to those sites that most likely contain the information requested and present the list to you in that order, usually in groups of ten. 22. Directory SearchMost search engines also provide a directory or list of categories or topics such as Arts & Humanities，Business & Economics, Computers & Interne

47、t. In a directory search, also known as index search, you select a category that fits the information that you want. Another list of subtopics that relates to the topic you selected appears. You select the subtopic that best relates to your topic and another subtopic list appears. You continue to na

48、rrow your search in this manner until a list of Web sites appears. This list corresponds to the hit list previously discussed. As a general rule, if you are searching for general information, use the directory search approach. For example, to find general information about music, use a directory sea

49、rch beginning with the category Arts & Humanities. 6. 3 Search Tools上一页下一页返回If you are searching for specific information , use the key word approach. For example, if you were looking for a specific MP3 file, use a keyword search entering the album title and/or the artists name in the text selection

50、 box. A recent study by the NEC Research Institute found that any search engine includes only a fraction of the informational sources on the Web. Therefore, it is highly recommended that you use more than one search engine when researching important topics. Or, you could use a special type of search

51、 engine called a metasearch engine. 6. 3. 2 Metasearch EnginesOne way to research a topic is to visit the Web site for several individual search engines. At each site, enter the search instructions, wait for the hits to appear, review the list, and visit selected sites. This process can be quite tim

52、e consuming and duplicate responses from different search engines are inevitable. Metasearch engines offer an alternative. 6. 3 Search Tools上一页下一页返回Metasearch engines are programs that automatically submit your search request to several search engines simultaneously. The metasearch engine receives t

53、he results, eliminates duplicates, orders the hits, and then provides the edited list to you. There are several metasearch sites available on the Web. One of the best known is Metacrawler. 6. 3. 3 Specialized Search EnginesSpecialized search engines focus on subject-specific Web sites. Specialized s

54、ites can potentially save you time by narrowing your search. For example, lets say you are researching a paper about the fashion industry. You could begin with a general search engine like Yahoo! Or, you could go to a search engine that specialized specifically in fashion. 6. 3 Search Tools上一页返回 E-m

55、ail, or electronic mail, refers to the transmission of messages over communication networks. E-mail uses the office memo paradigm in which a message contains a header that specifies the sender, recipients, and subject, followed by a body that contains the text of the message. To participate in E-mai

56、l , a person must assign a mailbox, which is in fact a storage area where messages can be placed. Each mailbox has an address in the form of mary_smithyahoo. com. An E-mail address is a string divided into two parts by thecharacter ( pronounced as “at” ) . The first part is a mailbox identifier, and

57、 the second stands for the name of the computer on which the mailbox resides. Mailbox identifiers are assigned locally, and only have significance on one computer. On some computer systems, the mailbox identifier is the same as a users login account identifier；on other systems, the two are independe

58、nt. The computer name in an E-mail address is a domain name. 6. 4 E-mail下一页返回Although it was originally intended to provide communication between pairs of people , computer programs can be used to send, receive, or forward E-mail. A mail exploder program uses a database of mailing lists to provide c

59、ommunication among large groups of participants. When a message is sent to a mailing list, the exploder forwards a copy to each member of the list. It is possible to build a program that automates list management. The program accepts a request to create or change a specified mailing list by adding o

60、r removing a participants address. You can also use E-mail to communicate with people you do not know but with whom you wish to share ideas and interests. You can participate in discussions and debates that range from general topics like current events and movies to specialized forums like computer