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A uniform resource locator (URL), colloquially known as an address on the
Web Web most often refers to: * Spider web, a silken structure created by the animal * World Wide Web or the Web, an Internet-based hypertext system Web, WEB, or the Web may also refer to: Computing * WEB, a literate programming system created by ...
, is a reference to a 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 A Uniform Resource Identifier (URI) is a unique sequence of characters that identifies a logical or physical resource used by web technologies. URIs may be used to identify anything, including real-world objects, such as people and places, conc ...
(URI), although many people use the two terms interchangeably. URLs occur most commonly to reference web pages ( HTTP/ HTTPS) but are also used for file transfer ( FTP), email ( mailto), database access ( JDBC), and many other applications. Most web browsers display the URL of a web page above the page in an address bar. A typical URL could have the form http://www.example.com/index.html, which indicates a protocol (http), a hostname (www.example.com), and a file name (index.html).


History

Uniform Resource Locators were defined in in 1994 by
Tim Berners-Lee Sir Timothy John Berners-Lee (born 8 June 1955), also known as TimBL, is an English computer scientist best known as the inventor of the World Wide Web. He is a Professorial Fellow of Computer Science at the University of Oxford and a profess ...
, the inventor of the World Wide Web, and the URI working group of the Internet Engineering Task Force (IETF), as an outcome of collaboration started at the IETF Living Documents
birds of a feather ''Birds of a Feather'' is a British sitcom originally broadcast on BBC One from 16 October 1989 to 24 December 1998, then revived on ITV from 2 January 2014 to 24 December 2020. The series stars Pauline Quirke and Linda Robson, with Lesley Jos ...
session in 1992. The format combines the pre-existing system of domain names (created in 1985) with file path syntax, where slashes are used to separate
directory Directory may refer to: * Directory (computing), or folder, a file system structure in which to store computer files * Directory (OpenVMS command) * Directory service, a software application for organizing information about a computer network's u ...
and
filename A filename or file name is a name used to uniquely identify a computer file in a directory structure. Different file systems impose different restrictions on filename lengths. A filename may (depending on the file system) include: * name &ndas ...
s. Conventions already existed where server names could be prefixed to complete file paths, preceded by a double slash (//). Berners-Lee later expressed regret at the use of dots to separate the parts of the domain name within
URI Uri may refer to: Places * Canton of Uri, a canton in Switzerland * Úri, a village and commune in Hungary * Uri, Iran, a village in East Azerbaijan Province * Uri, Jammu and Kashmir, a town in India * Uri (island), an island off Malakula Islan ...
s, wishing he had used slashes throughout, and also said that, given the colon following the first component of a URI, the two slashes before the domain name were unnecessary. Early WorldWideWeb collaborators including Berners-Lee originally proposed the use of UDIs: Universal Document Identifiers. An early (1993) draft of the HTML Specification referred to "Universal" Resource Locators. This was dropped some time between June 1994 () and October 1994 (draft-ietf-uri-url-08.txt). In his book '' Weaving the Web'', Berners-Lee emphasizes his preference for the original inclusion of "universal" in the expansion rather than the word "uniform", to which it was later changed, and he gives a brief account of the contention that led to the change.


Syntax

Every HTTP URL conforms to the syntax of a generic URI. A web browser will usually dereference a URL by performing an HTTP request to the specified host, by default on port number 80. URLs using the https scheme require that requests and responses be made over a secure connection to the website.


Internationalized URL

Internet users are distributed throughout the world using a wide variety of languages and alphabets, and expect to be able to create URLs in their own local alphabets. An Internationalized Resource Identifier (IRI) is a form of URL that includes Unicode characters. All modern browsers support IRIs. The parts of the URL requiring special treatment for different alphabets are the domain name and path. The domain name in the IRI is known as an Internationalized Domain Name (IDN). Web and Internet software automatically convert the domain name into
punycode Punycode is a representation of Unicode with the limited ASCII character subset used for Internet hostnames. Using Punycode, host names containing Unicode characters are transcoded to a subset of ASCII consisting of letters, digits, and hyphens, wh ...
usable by the Domain Name System; for example, the Chinese URL http://例子.卷筒纸 becomes http://xn--fsqu00a.xn--3lr804guic/. The xn-- indicates that the character was not originally ASCII. The URL path name can also be specified by the user in the local writing system. If not already encoded, it is converted to UTF-8, and any characters not part of the basic URL character set are escaped as
hexadecimal In mathematics and computing, the hexadecimal (also base-16 or simply hex) numeral system is a positional numeral system that represents numbers using a radix (base) of 16. Unlike the decimal system representing numbers using 10 symbols, hexa ...
using percent-encoding; for example, the Japanese URL http://example.com/引き割り.html becomes http://example.com/%E5%BC%95%E3%81%8D%E5%89%B2%E3%82%8A.html. The target computer decodes the address and displays the page.


Protocol-relative URLs

Protocol-relative links (PRL), also known as protocol-relative URLs (PRURL), are URLs that have no protocol specified. For example, //example.com will use the protocol of the current page, typically HTTP or HTTPS.


See also

*
Hyperlink In computing, a hyperlink, or simply a link, is a digital reference to data that the user can follow or be guided by clicking or tapping. A hyperlink points to a whole document or to a specific element within a document. Hypertext is text wit ...
* PURL – Persistent URL *
CURIE In computing, a CURIE (or ''Compact URI'') defines a generic, abbreviated syntax for expressing Uniform Resource Identifiers (URIs). It is an abbreviated URI expressed in a compact syntax, and may be found in both XML and non-XML grammars. A CURIE ...
(Compact URI) * URI fragment * Internet resource locator (IRL) * Internationalized Resource Identifier (IRI) * Clean URL * Typosquatting *
Uniform Resource Identifier A Uniform Resource Identifier (URI) is a unique sequence of characters that identifies a logical or physical resource used by web technologies. URIs may be used to identify anything, including real-world objects, such as people and places, conc ...
* URI normalization * Use of slashes in networking


Notes


Citations


References

* * * * * * * * * * * * * * * *


External links


URL specification
at WHATWG
URL splitter
that splits any URI into its parts {{Authority control Identifiers Internet properties established in 1994