Uniform Resource Locator (URL)

A web page on the Internet is uniquely identified by its address, called URL. URL is the address on the Internet at which the web page resides. The user uses this address to get a web page from the Internet. The general form of URL is

protocol://address/path where,

· protocol defines the method used to access the web page, e.g., http, ftp, news etc.

· address is the Internet address of the server where the web page resides. It contains the service (e.g. www) and the domain name (e.g. google.com), and

· path is the location of web page on the server.

To access documents on WWW, the HTTP protocol is used. An example of a URL is,

http://www.dsc.com/mainpage

where, http is the protocol, www.dsc.com is the address, and main page is the path.

                                                     An URL

Internet Search Engines

One of the most exciting things a user can do on the Internet is to search for information from multiple sources. There are hundreds of millions of web pages available, containing information on a wide variety of topics. There is no single catalogue maintained (similar to a library) that lists all the web pages and their information. The user needs to search the Internet to find the information relevant to his/her requirement. Internet Search engines or Search engines are specific web sites that help the users to find information stored on the Internet. Search engines search the Internet based on some important words (keywords) or combinations of words. Some of the common and well-known search engines are www.google.com, www.lycos.com and www.yahoo.com Using the Search Engine: The user uses the search engine as follows:

· Enter the address of search engine, for example www.google.com

· Enter the word, or combinations of words, or symbols with words, based on which the Internet is to be searched. Some options for searching are shown in Table.

                              Search engine options

Working of Search Engine:

The search engines work as follows:

· Search engines maintain a data repository of words along with the URL’s at which these words are found.

· When the user uses the search engine to search for a word or group of words, the search engine checks its data repository and returns a list of URLs that satisfy the search.

· To narrow down the scope of search, the search engines also provide different criteria for search. For example, some of the search criteria provided by Google search engine are Images, News, and Scholar to search for images, news, and published papers, respectively.

· Sites like www.msn.com are metasearch engines. Such sites do not maintain their own data repository, but send the search request to other search engines. The search results are collected from different search engines and displayed to the user.

(a) Search engine “Bing” by Microsoft (b) Search result by “Bing”

WWW Development Languages

The web pages or web sites are written using web development languages. Generally, web development languages are required for developing the layout of the web site in a Graphical User Interface (GUI) based web editor, and to add interactivity to the web sites—at client side and at server side.

HTML, Dynamic HTML (DHTML), and eXtensible Markup Language (XML) are some of the programming languages used to design and develop the web pages. You can also use software like Dreamweaver, Microsoft Front page, or your common word processor, which have the ability to save your document as a web page, for designing and development of the web pages.

· HTML is a descriptive language that uses tags or element to convert text into hypertext. HTML allows embedding of text, images, sound, graphics etc., and, also hyperlinks, to link to other web pages. HTML can include, or load scripts written in languages such as Javascript.

· DHTML is a collection of technologies that allows creation of dynamic web pages. In a dynamic web page, the structure, style, and content of the page loaded on the browser can be changed without having to request a new page from the browser. DHTML uses static markup language like HTML, cascading style sheets, scripting languages like Javascript, and Document Object Model (DOM).

· XML resembles HTML. However, XML allows the author to define unlimited number of tags. XML provides greater flexibility to the author, and has several advantages over HTML.

In client-side interactivity, the changes in the code for user interaction happen on the computer of the client side only. For example, if you are viewing a book store website, then as you move the cursor on a book, you can see a blurb showing the details of the book; this is implemented for client side.

· Scripting languages are used for client-side programming.

· Javascript, Java applets, and VBscript by Microsoft (works only in Internet Explorer), are some client-side scripting languages. Nowadays AJAX, a combination of XML and Javascript is also being used.

· The client-side script may not be allowed to access the client computer beyond the browser application, due to security reasons. ActiveX controls can be used to overcome this restriction. (ActiveX controls may harm your computer).

· Javascript code is included in the HTML code and is executed when you download the web page

The server-side interactivity involves the server that is hosting the web site. Here, one may need to access the database, or some other content stored on the server. For example, from the book store web site you decide to purchase a book. This may require filling in a form to check the availability of the book and completing the payment transaction; this requires server-side programming.

· Practical Extraction and Reporting Language (Perl), Hypertext Pre-processor (PHP), server side VBscript, Java Server Pages (JSP), Active Server Pages (ASP), and Ruby on Rails are some server side programming languages.

The Common Gateway Interface (CGI) allows scripting languages to control the web servers. Scripting languages that make use of CGI include Perl, ASP, and PHP.