What is URL (Uniform Resource Locator)

A URL (Uniform Resource Locator), as the name suggests, provides a way to locate a resource on the web, the hypertext system that operates over the internet. The URL contains the name of the protocol to be used to access the resource and a resource name. The first part of a URL identifies what protocol to use. The second part identifies the IP address or domain name where the resource is located.

A URL is the most common type of Uniform Resource Identifier (URI). URIs are strings of characters used to identify a resource over a network.

URL protocols include HTTP (Hypertext Transfer Protocol) and HTTPS (HTTP Secure) for web resources, "mailto" for email addresses, "ftp" for files on a File Transfer Protocol (FTP) server, and telnet for a session to access remote computers.

A URL is mainly used to point to a webpage, a component of a webpage or a program on a website. The resource name consists of:

• A domain name identifying a server or the web service; and
• A program name or a path to the file on the server.

Optionally, it can also specify:

• A network port to use in making the connection; or
• A specific reference point within a file -- a named anchor in an HTML (Hypertext Markup Language) file.
For example, http://www.technology.com/rfc/rfc2396.htm specifies that:
• The resource is to be retrieved using the HTTP protocol (which powers the web) via a web browser;
• The resource is reached through the domain name system (DNS) name, which could be a single server, a load-balanced cluster of servers or a service running on a system with a different name); and
• The path to the specific resource is /rfc/rfc2396.htm.
In the following example, the URL would retrieve the file at the point marked with the named anchor "index": http://www.technology.com/rfc/rfc2396.htm#index

The following example -- https://delphicoracle.gr:45678/Prohesy?year=2020 -- specifies:

• Use of the encrypted (secure) version of HTTP: HTTPS;
• Use of a nonstandard port (45678) for the communication; and
• Invocation of a program, "Prohesy" with parameter "year" set to value "2020".

Finally, this example -- ftp://www.somecompany.com/WHITEPAPERS/widgets.ps -- specifies use of the FTP protocol to download a file.