Anatomy of a website

What the World Wide Web is and what are the major components that make it work ?

The World Wide Web operates using a client/server networking principle. When you enter the URL (the web address) of a web page into your browser and click on Go, you ask the browser to make an HTTP request of the particular computer having that address. On receiving this request, that computer retus (“serves”) the required page to you in a form that your browser can interpret and display. In the case of the Inteet, of course, the server and client computers may be located anywhere in the world.

How web servers and clients(browsers) interact

Your HTTP request contains several pieces of information needed so that your page may be correctly identified and served to you, including the following:

• The domain at which the page is stored (for example, mydomain.com)
• The name of the page (This is the name of a file in the web server’s file system—for example, mypage.html.)
• The names and values of any parameters that you want to send with your request

Anyone with some experience using the World Wide Web will be familiar with the term web page. The traditional user interface for websites involves the visitor navigating among a series of connected pages each containing text, images, and so forth, much like the pages of a magazine.

Generally, each web page is actually a separate file on the server. The collection of individual pages constituting a website is managed by a program called a web server.

A web server is a program that interprets HTTP requests and delivers the appropriate web page in a form that your browser can understand. Many examples are available, most running under either UNIX/Linux operating systems or under some version of Microsoft Windows.

Perhaps the best-known server application is the Apache Web Server from the Apache Software Foundation , an open source project used to serve millions of websites around the world.

The Apache Software Foundation home page displayed in Inteet Explorer.

Another example is Microsoft’s IIS (Inteet Information Services), often used on host computers running the Microsoft Windows operating system.

Server-side programs, scripts, or languages, refer to programs that run on the server computer. Many languages and tools are available for server-side programming, including PHP, Java, and ASP (the latter being available only on servers running the Microsoft Windows operating system). Sophisticated server setups often also include databases of information that can be addressed by server-side scripts.

The purposes of such scripts are many and various. In general, however, they all are designed to preprocess a web page before it is retued to you. By this we mean that some or all of the page content will have been modified to suit the context of your request—perhaps to display traintimes to a particular destination and on a specific date, or to show only those products from a catalog that match your stated hobbies and interests.

In this way server-side scripting allows web pages to be served with rich and varied content that would be beyond the scope of any design using only static pages—that is, pages with fixed content

A web browser is a program on a web surfer’s computer that is used to interpret and display web pages. The first graphical web browser, Mosaic, eventually developed into the famous range of browsers produced by Netscape.

The Netscape series of browsers, once the most successful available were eventually joined by Microsoft’s Inteet Explorer offering, which subsequently went on to dominate the market.

Recent competitive efforts, though, have introduced a wide range of competing browser products including Opera, Safari, Konqueror, and especially Mozilla’s Firefox, an open source web browser that has recently gained an enthusiastic following (see Figure).

Browsers are readily available for many computer operating systems, including the various versions of Microsoft Windows, UNIX/Linux, and Macintosh, as well as for other computing devices ranging from mobile telephones to PDAs (Personal Digital Assistants)and pocket computers.

The Firefox browser from Mozilla.org browsing the Firefox Project home page.

We have already discussed how server scripts can improve your web experience by offering pages that contain rich and varied content created at the server and inserted into the page before it is sent to you.

Client-side programming, on the other hand, happens not at the server but right inside the user’s browser after the page has been received. Such scripts allow you to carry out many tasks relating to the data in the received page, including performing calculations, changing display colors and styles, checking the validity of user input, and much more.

Nearly all browsers support some version or other of a client-side scripting language called JavaScript, which is an integral part of Ajax and is the language we’ll be using in this book for client-side programming.

Every computer connected to the Inteet has a unique numerical address (called an IP address) assigned to it. However, when you want to view a particular website in your browser, you don’t generally want to type in a series of numbers—you want to use the domain name of the site in question. After all, it’s much easier to remember www.somedomain.com than something like 198.105.232.4.

When you request a web page by its domain name, your Inteet service provider submits that domain name to a DNS server, which tries to look up the database entry associated with the name and obtain the corresponding IP address. If it’s successful, you are connected to the site; otherwise, you receive an error.

The many DNS servers around the Inteet are connected together into a network that constantly updates itself as changes are made. When DNS information for a website changes, the revised address information is propagated throughout the DNS servers of the entire Inteet, typically within about 24 hours