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.
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).
* 1 History * 2 Syntax * 3 Internationalized URL * 4 Protocol-relative URLs * 5 See also * 6 Notes * 7 Citations * 8 References * 9 External links
Uniform Resource Locators were defined in
Request for Comments (RFC)
1738 in 1994 by
Tim Berners-Lee , the inventor of the
World Wide Web
The format combines the pre-existing system of domain names (created in 1985) with file path syntax, where slashes are used to separate directory and file names. 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 URIs , 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.
Main article: Uniform resource identifier § Syntax
Every HTTP URL conforms to the syntax of a generic URI. A generic URI is of the form:
* The SCHEME, consisting of a sequence of characters beginning with
a letter and followed by any combination of letters, digits, plus (+),
period (.), or hyphen (-). Although schemes are case-insensitive, the
canonical form is lowercase and documents that specify schemes must do
so with lowercase letters. It is followed by a colon (:). Examples of
popular schemes include http(s) , ftp , mailto , file , data , and irc
* An AUTHORITY PART, comprising:
* An optional authentication section of a user name and password ,
separated by a colon, followed by an at symbol (@)
* A "HOST", consisting of either a registered name (including but
not limited to a hostname ), or an
* A PATH, which contains data, usually organized in hierarchical form, that appears as a sequence of segments separated by slashes. Such a sequence may resemble or map exactly to a file system path , but does not always imply a relation to one. The path must begin with a single slash (/) if an authority part was present, and may also if one was not, but must not begin with a double slash. The path is always defined, though the defined path may be empty (zero length), therefore no trailing slash.
QUERY DELIMITER EXAMPLE
Ampersand (&) key1=value1) key1=value1;key2=value2
* An optional QUERY, separated from the preceding part by a question
mark (?), containing a query string of non-hierarchical data. Its
syntax is not well defined, but by convention is most often a sequence
of attribute–value pairs separated by a delimiter .
* An optional FRAGMENT, separated from the preceding part by a hash
(#). The fragment contains a fragment identifier providing direction
to a secondary resource, such as a section heading in an article
identified by the remainder of the URI. When the primary resource is
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 will be made over a secure connection to the website .
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 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 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 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, either HTTP or HTTPS.
* ^ A
URL implies the means to access an indicated resource and is
denoted by a protocol or an access mechanism, which is not true of
every URI. Thus http://www.example.com is a URL, while
www.example.com is not.
* ^ The procedures for registering new
* ^ W3C (2009) .
* ^ RFC 3986 (2005) .
* ^ A B Joint W3C/IETF
* "Berners-Lee "sorry" for slashes". BBC News. 2009-10-14. Retrieved
* "Living Documents BoF Minutes".
World Wide Web
* Berners-Lee, Tim ; Masinter, Larry; McCahill, Mark (August 1998).
"Uniform Resource Locators (URL)".
Internet Engineering Task Force .
Retrieved 31 August 2015.
* Berners-Lee, Tim (2015) . "Why the //, #, etc?". Frequently asked
World Wide Web