Structure of the Internet: URIs

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UNIT 2 - ⇑ Structure of the Internet ⇑

← Domain names URIs Client server model →

Uniform Resource Identifier (URI) - A character string identifying a resource on the internet


Resources such as documents, files and folders sitting on the internet need a method to identify them and access them. URIs provide a way to linking to these resources. There are two types of URI, but you only need to know URL for the exam:

  • Uniform Resource Name (URN) - the name of a resource, but not its exact location.

e.g. urn:isbn:0486419266
The URN for R.U.R. (1921 play), identified by its book number.

  • Uniform Resource Locator (URL) - the exact location of a resource.

e.g. http://www.gutenberg.org/catalog/world/readfile?fk_files=85821
The project gutenberg page for the R.U.R. book

Diagram of URI scheme categories. A Uniform Resource Name (URN) functions like a person's name, while a Uniform Resource Locator (URL) resembles that person's street address. In other words: the URN defines an item's identity, while the URL provides a method for finding it.

Uniform Resource Locator (URL)[edit]

Uniform Resource Locator - A character string referring to the location of an internet resource


A URL is a URI that, "in addition to identifying a resource, provides a means of locating the resource by describing its primary access mechanism (e.g., its network location)"[1]. URLs allow us to specify the domain name and exact location of a resource on the internet. For example, the following links to a picture on wikicommons:

http://commons.wikimedia.org/wiki/File:George_Clausen_WWI_poster.jpg

We can break this down into its constituent parts:

\underbrace{http://}_\text{protocol} \underbrace{commons.wikimedia.org}_\text{hostname} \underbrace{/wiki/File:George_{-}Clausen_{-}WWI_{-} poster.jpg}_\text{location on server}

We can therefore summarise a URL as follows:

protocol://hostname/location_-of_-file
Exercise: Uniform Resource Identifiers

Describe the difference between a URN and a URL

Answer :

  • URN gives the name of a resource, but not necessarily its location
  • URL gives the location of a resource

Give the 3 parts that make up a URL

Answer :

  • the protocol
  • the hostname
  • the file location

For the following address:

http://www2.example.gov.uk/

describe the parts:

  • http://
  • www2
  • gov.uk
  • example

Answer :

  • http:// - the protocol being used
  • www2 - the name of the host being used
  • gov.uk - the domain name is registered in the uk, and is a governmental organisation
  • example - the domain name of the government organisation

References[edit]

  1. Tim Berners-Lee, Roy T. Fielding, Larry Masinter. (January 2005). “Uniform Resource Identifier (URI): Generic Syntax”. Internet Society. RFC 3986; STD 66.