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What is a URL: Uniform Resource Locator

Last Edit: 10/01/17

URL stands for Uniform Resource Locator. URL's are character strings that are primarily used to locate webpages. The URL syntax was standardised in 1994 by:

  1. Tim Berners-Lee (Inventor of the World Wide Web)
  2. Internet Engineering Task Force (IETF) (Maintain URI system)

URL's are a type of Uniform Resource Identifier (URI). While URI's are used to locate a massive array of resources on the Internet, URL's are primarily used to locate resources on the World Wide Web. URL's can also be used to locate files (via ftp) and email (via mailto). How HTTP functions, in relation to URL's, was outlined in: RFC 1738, RFC 2616, and RFC 2068.

Syntax of a World Wide Web URL

The URL syntax was standardised in 1994, and consists of the following:

  1. dots "." to separate the parts of a hostname and domain name.
  2. slashes "/" to separate directory and file names.
  3. a colon and two slashes "://" that follows the schema name.

The above syntax elements can be found within the following URL (this document):

http://www.internet-guide.co.uk/url.html

However, as you can tell, the URL includes some other elements, which are:

  1. Schema name (http): which is the Hypertext Transfer Protocol.
  2. Fully qualified domain name (FQDN) (www.internet-guide.co.uk)
  3. Domain name (internet-guide.co.uk)
  4. Filename (url.html): document located at the above domain name.

A fully qualified domain name (FQDN) consists of the host (www), the namespace (internet-guide), and a top level domain (uk). It is also possible to refer to (www), (www.internet-guide.co.uk) and (internet-guide.co.uk) as a hostname: as each is associated with an IP address (host computer).

However, if the domain name (internet-guide.co.uk) was not associated with an IP address: it would not be a hostname, just a domain name. When (internet-guide.co.uk) is associated with an IP address it would be a hostname and a domain name. However, for the domain name (internet-guide.co.uk) to be a fully qualified domain name, it would need to include it's local hostname (www) and would be written as (www.internet-guide.co.uk).

Hostnames have to conform to the following specification:

  1. Use either: ASCII letters, Numbes 0-9, and hyphens ('-').
  2. Each label (internet-guide) has to be between 1 and 63 characters.
  3. Complete hostnames can only be 255 characters.