From the client’s point of view, all that is needed is a Web browser and an Internet connection in order to get on the Web. From the server’s point of view, what is needed is a machine that is connected to the Internet, runs Web server software and hosts the required documents. 2 The Web uses the Internet as its underlying network medium. Data exchanged between Web clients and servers travel over the Internet. However, the Internet and the Web are not one and the same. There are many other services aside from the Web which run over the Internet. Self-test 1.2 1 Three new technologies were created to build the Web: • The HyperText Markup Language (HTML) defines how webpages and hypertext links are written. • Universal Resource Locators (URLs) define the Web’s system for addressing and locating documents. Hypertext links contain URLs. • The HyperText Transfer Protocol (HTTP) is the communication language or protocolbetween the Web client (the Web browser) and the Web server. It describes how clients make requests for information and how servers respond to them. 2 Hypertext is a system of a collection of documents that are associated through active links. When a user chooses a link, that link is followed, and the document that link pointed to is fetched and displayed. Hypertext is a non-linear text system that creates an ‘information space.’ 3 A URL is the addressof a unique location of an Internet resource. For example, is the URL for the Lycos search engine and is the URL for NCSA’s FTP site. 4 Hypertext links are represented as anchor tags in HTML. An anchor tag takes this form in HTML: <A HREF=""> The Open University of Hong Kong</A>
46COMP S834 Web Server Technology 5 An inline image takes this form in an HTML document: <IMG SRC = "picture.gif"> 6 These HTML tags should always be in an HTML document: <HTML></HTML> <HEAD><TITLE></TITLE></HEAD> <BODY></BODY> Self-test 1.3 1 There are two design characteristics that can help the Internet withstand catastrophic attacks in wartime. First, it is decentralized. Computers can communicate directly with each other without having to go through a central node. This ensures that communication can still take place even if some machines are destroyed. Second, the Internet is a packet-switching network which offersmultiple, redundant routesbetween two endpoints. This ensures that packets can still be routed between two hosts even if certain sections of the network are rendered inoperable. 2 The Internet is a global network that is made up of many smaller networks. These smaller networks connect with each other to form bigger and higher-level networks. There is no overall controlling network. Instead, these higher-level networks connect to each other through Network Access Points (NAPs). The Internet is a collection of huge networks which implement the same protocols and agree to route data traffic to each other at these Network Access Points.
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