A Uniform Resource Locator (URL), colloquially termed a web address, is a reference to a web resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identifier (URI), although many people use the two terms interchangeably. URLs occur most commonly to reference web pages (HTTP) but are also used for file transfer (FTP), email (mailto), database access (JDBC), and many other applications.
A URL contains four or more groups of words, where each group represents a specific component of the URL. Each group or component specifies a particular information about URL. The four components of a URL are: protocol, type of network, domain name and domain extension.
The first component of a URL normally represents the protocol being followed for communication between the server and the computer on which the URL is being accessed. A protocol defines the standards for communication and data transfer between two computers ( or other electronic devices ). Let's take an example to understand the concept of protocol better. You must have attended a telephone call. Let's recollect the procedure of attending a phone call:
- A caller dials your number and your phone rings.
- You receive the phone call.
- You greet the caller by saying "Hello".
- The caller replies to the greeting.
- The conversation between you and the caller continues.
- After the conversation is over, you wish the caller good-bye.
- The caller replies and disconnects the phone.
If you closely observe these steps, they are generally common for all types of phone calls. In other words, these steps define the standard to communicate on the phone.
When you request for a Web page or transfer files over a network using computers, communication takes place between two computers. That is, your computer establishes a connection with the specific server (that is also a computer) containing the web page or file that you want to access. It then requests for the specified Web page or file. This procedure is similar to the procedure of attending a phone call. Therefore, like the standard used for communicating over the phone, computers also require certain standards to communicate with each other. These standards of communication are called protocols.
Hypertext transfer protocol (HTTP) and File Transfer Protocol (FTP) are examples of protocols used for communication between computers. When you access a website, you generally use the HTTP protocol. FTP is used as a protocol when you want to transfer or access file over a network.
In any typical URL, such as http://www.example.com, the https is used to identify the protocol and server according to the standard URL syntax, a colon(:) and two forward slashes (//) follow the protocol/server.
List of Internet Protocols
|ftp||File Transfer Protocol||Used for text and binary files, which are arranged in a hierarchical structure.|
|gopher||Transfer Control Protocol / Internet Protocol (TCP/IP)||Used for text and binary files, which are arranged in a menu structure.|
|http||Hypertext transfer protocol||Used for hypertext / hypermedia (multimedia) files.|
|Post Office Protocol (POP) version 3 and Simple Mail Transfer Protocol (SMTP)||Used for messages sent through e-mails.|
|news||Network New Transfer Protocol (NNTP)||Used for newsgroups.|
Type of Network
Observe that www is second component of the URL http://www.example.com. The term www specifies that the website that you want to access is on the internet. Moreover, note that in a URL, the protocol and the type of network are separated by a colon and two forward slashes (://).
Domain name is the third component of a URL, and represents the name of one or more computers that act as servers on the Internet. For example, in the URL http://www.example.com, example specifies the domain name. A large website, such as Google or Yahoo!, uses more than one computer and the entire group of computers acts as a single server. A domain name must be registered so that one domain name does not represent more than one server. Special administrative bodies, called domain registrars, register the domain name. After a domain name is registered with domain registrar, the domain name cannot be used by any other website.
The fourth component of the URL is domain extension, which specifies the type of website. The domain extension of a URL uses standard codes to represent the type of website. For example, com is used to specify that the website is created for commercial purposes.
|Type of Website||Extension||Description|
|Commercial||com||Specifies a commercial website, such as http://www.yahoo.com.|
|Non-profit Organization||org||Specifies a website created for non-profit ventures, such as http://www.wikipedia.org.|
|Country-specific||co.gh||Specifies a website that is specific to a country. For example, co.gh represents the domain extension of a commercial website specific to Ghana.|
|Government||gov||Specifies a website that belongs to government of a country, such as http://www.india.gov.in|
Just like the example of Ghana in the preceding table, two URLs of country-specific websites for India and Japan are given below:
- http://www.yahoo.co.in: In this URL, in represents the abbreviation of India, which means that this URL is based in India.
- http://www.yahoo.co.jp: In this URL, jp represents the abbreviation of Japan, which means that this URL is based in Japan.