06-02-2013, 09:56 AM
Introduction to Java and Web Design
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Introduction
The World Wide Web is abbreviated as “www” and is quite a familiar word which we commonly use while using the Internet. Most of us use the Internet for some or the other reason in our day to day activities in offices, homes, banks and so on, and every time we use the Internet without our knowledge, we use “www”. So what is this “www” and how does it work? This unit will help you understand how the Web works and its basic features. We will also learn the difference between the Internet and Web.
A Web browser enables you to access the Web; in this unit we will study what is a Web browser and also analyse the different browsers available.
We will also discuss the origin of Java and also its significance. We also briefly discuss about Java applications such as Java servlets and JSP that we can use for Web designing. We will also learn about the most popular tool on the Web, the search engine in this unit.
Learning Objectives:
After studying this unit, you should be able to:
• explain the difference between the Web and the Internet.
• describe the purpose of a browser.
• analyse the structure of a Web page in a browser.
• explain the importance of Java in Web designing.
• learn the uses and performance of search engine.
World Wide Web
World Wide Web is popularly known as "Web". It is defined as "wide area information retrieval initiative aiming to give universal access to a large universe of information." Thus, Web is an Internet based network of computers, which allows users of one computer, to access information saved on another’s computer, through a worldwide network called the Internet. The Web is a collection of a group of graphics and text files called the Web pages (refer sub section 1.3.2 to know more about Web pages). We also need to know that a Web page is a single Hyper Text Marker Language (HTML) text file consisting of one or more graphics along with some additional features to make the Web page more user friendly. These Web pages are combined and linked together logically to form Websites.
We usually define Web with the help of two specifications the Hyper Text Transfer Protocol (HTTP) and Hyper Text Markup Language (HTML). The most interesting concept of Web is the hypertext, where a hypertext is the text that enables you to link to other parts of the text and other information. For example, consider that you are searching for some information in the Google search engine. First, you will enter the key word (search term) of your search item and click the search button to start the search. Later, a number of blue coloured texts appear on the screen. These blue coloured texts are called the hyperlinks. When you click this link, the browser opens the respective Web pages.
The name "Web" was coined because the structure in which all the texts linked in this system resembled a spider's Web. So how exactly this Web works? The concept is very simple every Web page has its own unique address also known as the Uniform Resource Locator (URL). An URL is a unique address given to a Web page, using which we can access the page on the Web. When you type the URL in the browser, the browser will connect to the Web page and the page appears on your screen. For example, when you enter the URL [http:// www. smude. edu.in/ Pages/Welcome.aspx] then your browser connects to the Sikkim Manipal University (SMU) server and sends a request for the page. The server machine receiving the request sends back the SMU home page URL.
Internet versus web
We understood what is World Wide Web. Let us now discuss the difference that exists between the Internet and Web. Many get confused with the Internet and Web and during a casual conversation we use it in such a way that there is no difference between them. However, this is not right. The Internet and Web are two different entities. Web is one of the services available on the Internet. As we know, Web comprises of Web pages and these pages are transported in the form of information packets on the Internet. For example, the “Web” can be compared to a “train” running on the “rails” called the “Internet”.
The Internet comprises of a huge hardware network which can be accessed by everyone across the world. The network is further divided into sub-networks, which consist of a number of computers transmitting data in the form of information packets. The computers establish a connection using fibre optical cables, copper wires or wireless connection and these connections form the network. However, Web is the software that functions on the Internet. As we have studied, it is a collection of Web pages, which are linked through URLs and hyperlinks. Therefore, it is termed as the service provided by the Internet just like other services such as file transfer, chat, e-mail and so on. Therefore, we can say that the Internet is independent of Web whereas, Web is dependent on the Internet.
One more major difference between the Internet and Web is the protocol suite that they use. The Internet is governed by the Internet Protocol (IP) which is the primary communication protocol used for transmitting data packets across the network. However, Web is governed by the Hyper Text Transfer Protocol (HTTP) which links various resources like the files, documents and so on of the Web.
Web Browsers
We learnt that Web comprises of a number of text files that are linked to each other is a specific manner and these text files are called HTML Web pages. You can view these Web pages with the help of a Web browser. Therefore, a browser is a software program that enables you to view and interact with any information available on the Web. In general, the term browser is a user interface that allows you to navigate through and read text files online. The browser program is used to make a Web page or Website request to a Web server through the Internet using the URL of the respective Web page or Web site.
The “WorldWideWeb” created in 1990 was the first Web browser. However, later this name was changed to Nexus to avoid confusion with the World Wide Web. Today, there are a number of Web browsers available in the market for example, the Internet Explores (IE), Firefox, Flock, Web 2.0, Safari, Opera, and so on.
Let us now study the two main functions of a Web browser:
• To make a request for a page from a computer. You can do this by typing the URL of the page in the address field of the browser. Even when you click on a hyperlink the similar action that of accessing the Web page associated with the URL is performed by the browser.
• To interpret the HTML page sent back by the Web server. This is done because the HTML text received from the Web server is in the American Standard Code for Information Interchange (ASCII) form. The Web browser, after receiving this text interprets it and creates the page in its original form.
The HTML and Cascading Style Sheets (CSS) specifications (refer Unit 4), specifies the way in which the browser interprets and displays the HTML files. The World Wide Web Consortium organisation monitors the standards of the Web and helps to maintain the browser specifications defined by HTML and CCS.
Browser components
Now let us learn the architecture of a Web browser with the help of reference architecture. This reference architecture is the basic architecture for Web browsers and helps you to easily understand the various components that exist in the Web browser.