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URL

January 10, 2023

For other uses, see URL (disambiguation).

A Uniform Resource Locator (URL), colloquially termed as a web address,[1] 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),[2][3] although many people use the two terms interchangeably.[4][a] 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.

URL
Uniform Resource Locator
AbbreviationURL
StatusPublished
First published1994; 29 years ago (1994)
Latest versionLiving Standard
2022
OrganizationInternet Engineering Task Force (IETF)
CommitteeWeb Hypertext Application Technology Working Group (WHATWG)
SeriesRequest for Comments (RFC)
EditorsAnne van Kesteren
AuthorsTim Berners-Lee
Base standards
  • RFC 3986. – Uniform Resource Identifier (URI): Generic Syntax.
  • RFC 4248. – The telnet URI Scheme.
  • RFC 4266. – The gopher URI Scheme.
  • RFC 6068. – The ‘mailto’ URI Scheme.
  • RFC 6196. – Moving mailserver: URI Scheme to Historic.
  • RFC 6270. – The ‘tn3270’ URI Scheme.
Related standardsURI, URN
DomainWorld Wide Web
LicenseCC BY 4.0
Websiteurl.spec.whatwg.org

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 RFC 1738 in 1994 by Tim Berners-Lee, the inventor of the World Wide Web, and the URI working group of the Internet Engineering Task Force (IETF),[7] as an outcome of collaboration started at the IETF Living Documents birds of a feather session in 1992.[7][8]

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 filenames. Conventions already existed where server names could be prefixed to complete file paths, preceded by a double slash (//).[9]

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,[9] and also said that, given the colon following the first component of a URI, the two slashes before the domain name were unnecessary.[10]

An early (1993) draft of the HTML Specification[11] referred to "Universal" Resource Locators. This was dropped some time between June 1994 (RFC 1630) and October 1994 (draft-ietf-uri-url-08.txt).[12]

Syntax

Main article: Uniform Resource Identifier § Syntax

Every HTTP URL conforms to the syntax of a generic URI. The URI generic syntax consists of five components organized hierarchically in order of decreasing significance from left to right:[13]

URI = scheme ":" ["//" authority] path ["?" query] ["#" fragment]

A component is undefined if it has an associated delimiter and the delimiter does not appear in the URI; the scheme and path components are always defined.[14] A component is empty if it has no characters; the scheme component is always non-empty.[13]

The authority component consists of subcomponents: 

authority = [userinfo "@"] host [":" port]

This is represented in a syntax diagram as:

 

The URI comprises:

  • A non-empty scheme component followed by a colon (:), 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. Examples of popular schemes include http, https, ftp, mailto, file, data and irc. URI schemes should be registered with the Internet Assigned Numbers Authority (IANA), although non-registered schemes are used in practice.[b]
  • An optional authority component preceded by two slashes (//), comprising:
    • An optional userinfo subcomponent followed by an at symbol (@), that may consist of a user name and an optional password preceded by a colon (:). Use of the format username:password in the userinfo subcomponent is deprecated for security reasons. Applications should not render as clear text any data after the first colon (:) found within a userinfo subcomponent unless the data after the colon is the empty string (indicating no password).
    • A host subcomponent, consisting of either a registered name (including but not limited to a hostname) or an IP address. IPv4 addresses must be in dot-decimal notation, and IPv6 addresses must be enclosed in brackets ([]).[16][c]
    • An optional port subcomponent preceded by a colon (:), consisting of decimal digits.
  • A path component, consisting of a sequence of path segments separated by a slash (/). A path is always defined for a URI, though the defined path may be empty (zero length). A segment may also be empty, resulting in two consecutive slashes (//) in the path component. A path component may resemble or map exactly to a file system path but does not always imply a relation to one. If an authority component is defined, then the path component must either be empty or begin with a slash (/). If an authority component is undefined, then the path cannot begin with an empty segment—that is, with two slashes (//)—since the following characters would be interpreted as an authority component.[18]
By convention, in http and https URIs, the last part of a path is named pathinfo and it is optional. It is composed by zero or more path segments that do not refer to an existing physical resource name (e.g. a file, an internal module program or an executable program) but to a logical part (e.g. a command or a qualifier part) that has to be passed separately to the first part of the path that identifies an executable module or program managed by a web server; this is often used to select dynamic content (a document, etc.) or to tailor it as requested (see also: CGI and PATH_INFO, etc.).
Example:
URI: "http://www.example.com/questions/3456/my-document"
where: "/questions" is the first part of the path (an executable module or program) and "/3456/my-document" is the second part of the path named pathinfo, which is passed to the executable module or program named "/questions" to select the requested document.
An http or https URI containing a pathinfo part without a query part may also be referred to as a 'clean URL' whose last part may be a 'slug'.
Query delimiter Example
Ampersand (&) key1=value1&key2=value2
Semicolon (;)[d] key1=value1;key2=value2
  • An optional query component preceded by a question mark (?), consisting of 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 component preceded 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 an HTML document, the fragment is often an id attribute of a specific element, and web browsers will scroll this element into view.

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.[20][21]

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.[22]

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.[20]

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.[23][24]

See also

Notes

  1. ^ 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.[5][4] Thus http://www.example.com is a URL, while www.example.com is not.[6]
  2. ^ The procedures for registering new URI schemes were originally defined in 1999 by RFC 2717, and are now defined by RFC 7595, published in June 2015.[15]
  3. ^ For URIs relating to resources on the World Wide Web, some web browsers allow .0 portions of dot-decimal notation to be dropped or raw integer IP addresses to be used.[17]
  4. ^ Historic RFC 1866 (obsoleted by RFC 2854) encourages CGI authors to support ';' in addition to '&'.[19]

Citations

  1. ^ W3C (2009).
  2. ^ "Forward and Backslashes in URLs". zzz.buzz. Retrieved 2018-09-19.
  3. ^ RFC 3986 (2005).
  4. ^ a b Joint W3C/IETF URI Planning Interest Group (2002).
  5. ^ RFC 2396 (1998).
  6. ^ Miessler, Daniel. "The Difference Between URLs and URIs".
  7. ^ a b W3C (1994).
  8. ^ IETF (1992).
  9. ^ a b Berners-Lee (2015).
  10. ^ BBC News (2009).
  11. ^ Berners-Lee, Tim; Connolly, Daniel "Dan" (March 1993). Hypertext Markup Language (draft RFCxxx) (Technical report). p. 28.
  12. ^ Berners-Lee, Tim; Masinter, Larry; McCahill, Mark Perry (October 1994). Uniform Resource Locators (URL) (Technical report). (This Internet-Draft was published as a Proposed Standard RFC, RFC 1738 (1994)) Cited in Ang, C. S.; Martin, D. C. (January 1995). Constituent Component Interface++ (Technical report). UCSF Library and Center for Knowledge Management.
  13. ^ a b RFC 3986 (2005), §3.
  14. ^ RFC 3986 (2005), §5.2.1.
  15. ^ IETF (2015).
  16. ^ RFC 3986 (2005), §3.2.2.
  17. ^ Lawrence (2014).
  18. ^ RFC 2396 (1998), §3.3.
  19. ^ RFC 1866 (1995), §8.2.1.
  20. ^ a b W3C (2008).
  21. ^ W3C (2014).
  22. ^ IANA (2003).
  23. ^ Glaser, J. D. (2013). Secure Development for Mobile Apps: How to Design and Code Secure Mobile Applications with PHP and JavaScript. CRC Press. p. 193. ISBN 978-1-48220903-7. Retrieved 2015-10-12.
  24. ^ Schafer, Steven M. (2011). HTML, XHTML, and CSS Bible. John Wiley & Sons. p. 124. ISBN 978-1-11808130-3. Retrieved 2015-10-12.

References

External links

January 10, 2023
other, uses, disambiguation, uniform, resource, locator, colloquially, termed, address, reference, resource, that, specifies, location, computer, network, mechanism, retrieving, specific, type, uniform, resource, identifier, although, many, people, terms, inte. For other uses see URL disambiguation A Uniform Resource Locator URL colloquially termed as a web address 1 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 2 3 although many people use the two terms interchangeably 4 a 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 URLUniform Resource LocatorAbbreviationURLStatusPublishedFirst published1994 29 years ago 1994 Latest versionLiving Standard2022OrganizationInternet Engineering Task Force IETF CommitteeWeb Hypertext Application Technology Working Group WHATWG SeriesRequest for Comments RFC EditorsAnne van KesterenAuthorsTim Berners LeeBase standardsRFC 3986 Uniform Resource Identifier URI Generic Syntax RFC 4248 The telnet URI Scheme RFC 4266 The gopher URI Scheme RFC 6068 The mailto URI Scheme RFC 6196 Moving mailserver URI Scheme to Historic RFC 6270 The tn3270 URI Scheme Related standardsURI URNDomainWorld Wide WebLicenseCC BY 4 0Websiteurl wbr spec wbr whatwg wbr orgMost 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 Contents 1 History 2 Syntax 3 Internationalized URL 4 Protocol relative URLs 5 See also 6 Notes 7 Citations 8 References 9 External linksHistoryUniform Resource Locators were defined in RFC 1738 in 1994 by Tim Berners Lee the inventor of the World Wide Web and the URI working group of the Internet Engineering Task Force IETF 7 as an outcome of collaboration started at the IETF Living Documents birds of a feather session in 1992 7 8 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 filenames Conventions already existed where server names could be prefixed to complete file paths preceded by a double slash 9 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 9 and also said that given the colon following the first component of a URI the two slashes before the domain name were unnecessary 10 An early 1993 draft of the HTML Specification 11 referred to Universal Resource Locators This was dropped some time between June 1994 RFC 1630 and October 1994 draft ietf uri url 08 txt 12 SyntaxMain article Uniform Resource Identifier Syntax Every HTTP URL conforms to the syntax of a generic URI The URI generic syntax consists of five components organized hierarchically in order of decreasing significance from left to right 13 URI scheme authority path query fragment A component is undefined if it has an associated delimiter and the delimiter does not appear in the URI the scheme and path components are always defined 14 A component is empty if it has no characters the scheme component is always non empty 13 The authority component consists of subcomponents authority userinfo host port This is represented in a syntax diagram as The URI comprises A non empty scheme component followed by a colon 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 Examples of popular schemes include a href Hypertext Transfer Protocol html title Hypertext Transfer Protocol http a a href HTTP Secure html class mw redirect title HTTP Secure https a a href File Transfer Protocol html title File Transfer Protocol ftp a a href Mailto html title Mailto mailto a a href File URI scheme html title File URI scheme file a a href Data URI scheme html title Data URI scheme data a and a href Internet Relay Chat html URI scheme title Internet Relay Chat irc a URI schemes should be registered with the Internet Assigned Numbers Authority IANA although non registered schemes are used in practice b An optional authority component preceded by two slashes comprising An optional userinfo subcomponent followed by an at symbol that may consist of a user name and an optional password preceded by a colon Use of the format username password in the userinfo subcomponent is deprecated for security reasons Applications should not render as clear text any data after the first colon found within a userinfo subcomponent unless the data after the colon is the empty string indicating no password A host subcomponent consisting of either a registered name including but not limited to a hostname or an IP address IPv4 addresses must be in dot decimal notation and IPv6 addresses must be enclosed in brackets 16 c An optional port subcomponent preceded by a colon consisting of decimal digits A path component consisting of a sequence of path segments separated by a slash A path is always defined for a URI though the defined path may be empty zero length A segment may also be empty resulting in two consecutive slashes in the path component A path component may resemble or map exactly to a file system path but does not always imply a relation to one If an authority component is defined then the path component must either be empty or begin with a slash If an authority component is undefined then the path cannot begin with an empty segment that is with two slashes since the following characters would be interpreted as an authority component 18 By convention in http and https URIs the last part of a path is named pathinfo and it is optional It is composed by zero or more path segments that do not refer to an existing physical resource name e g a file an internal module program or an executable program but to a logical part e g a command or a qualifier part that has to be passed separately to the first part of the path that identifies an executable module or program managed by a web server this is often used to select dynamic content a document etc or to tailor it as requested see also CGI and PATH INFO etc Example URI http www example com questions 3456 my document where questions is the first part of the path an executable module or program and 3456 my document is the second part of the path named pathinfo which is passed to the executable module or program named questions to select the requested document dd An http or https URI containing a pathinfo part without a query part may also be referred to as a clean URL whose last part may be a slug Query delimiter ExampleAmpersand amp key1 value1 amp key2 value2Semicolon d key1 value1 key2 value2An optional query component preceded by a question mark consisting of 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 component preceded 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 an HTML document the fragment is often an id attribute of a specific element and web browsers will scroll this element into view 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 URLInternet 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 20 21 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 22 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 20 Protocol relative URLsProtocol 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 23 24 See alsoHyperlink PURL Persistent URL CURIE Compact URI Fragment identifier Internet Resource Locator IRL Internationalized resource identifier IRI Semantic URL Clean URL Typosquatting Uniform Resource Identifier URL normalization Use of slashes in networkingNotes 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 5 4 Thus http www example com is a URL while www example com is not 6 The procedures for registering new URI schemes were originally defined in 1999 by RFC 2717 and are now defined by RFC 7595 published in June 2015 15 For URIs relating to resources on the World Wide Web some web browsers allow 0 portions of dot decimal notation to be dropped or raw integer IP addresses to be used 17 Historic RFC 1866 obsoleted by RFC 2854 encourages CGI authors to support in addition to amp 19 Citations W3C 2009 Forward and Backslashes in URLs zzz buzz Retrieved 2018 09 19 RFC 3986 2005 a b Joint W3C IETF URI Planning Interest Group 2002 RFC 2396 1998 Miessler Daniel The Difference Between URLs and URIs a b W3C 1994 IETF 1992 a b Berners Lee 2015 BBC News 2009 Berners Lee Tim Connolly Daniel Dan March 1993 Hypertext Markup Language draft RFCxxx Technical report p 28 Berners Lee Tim Masinter Larry McCahill Mark Perry October 1994 Uniform Resource Locators URL Technical report This Internet Draft was published as a Proposed Standard RFC RFC 1738 1994 Cited in Ang C S Martin D C January 1995 Constituent Component Interface Technical report UCSF Library and Center for Knowledge Management a b RFC 3986 2005 3 RFC 3986 2005 5 2 1 IETF 2015 RFC 3986 2005 3 2 2 Lawrence 2014 RFC 2396 1998 3 3 RFC 1866 1995 8 2 1 a b W3C 2008 W3C 2014 IANA 2003 Glaser J D 2013 Secure Development for Mobile Apps How to Design and Code Secure Mobile Applications with PHP and JavaScript CRC Press p 193 ISBN 978 1 48220903 7 Retrieved 2015 10 12 Schafer Steven M 2011 HTML XHTML and CSS Bible John Wiley amp Sons p 124 ISBN 978 1 11808130 3 Retrieved 2015 10 12 References Berners Lee sorry for slashes BBC News 2009 10 14 Retrieved 2010 02 14 Living Documents BoF Minutes World Wide Web Consortium 1992 03 18 Retrieved 2011 12 26 Berners Lee Tim 1994 03 21 Uniform Resource Locators URL A Syntax for the Expression of Access Information of Objects on the Network World Wide Web Consortium Retrieved 2015 09 13 Berners Lee Tim Masinter Larry McCahill Mark Perry December 1994 Uniform Resource Locators URL doi 10 17487 RFC1738 RFC 1738 Retrieved 2015 08 31 Berners Lee Tim 2015 2000 Why the etc Frequently asked questions World Wide Web Consortium Retrieved 2010 02 03 Connolly Daniel Dan Sperberg McQueen C Michael eds 2009 05 21 Web addresses in HTML 5 World Wide Web Consortium Retrieved 2015 09 13 IANA 2003 02 14 Completion of IANA Selection of IDNA Prefix IETF Announce mailing list Archived from the original on 2004 12 08 Retrieved 2015 09 03 Berners Lee Tim Connolly Daniel Dan November 1995 Hypertext Markup Language 2 0 Internet Engineering Task Force doi 10 17487 RFC1866 S2CID 6628570 Retrieved 2015 09 13 a href Template Cite journal html title Template Cite journal cite journal a Cite journal requires journal help Berners Lee Tim Fielding Roy T Masinter Larry August 1998 Uniform Resource Identifiers URI Generic Syntax doi 10 17487 RFC2396 RFC 2396 Retrieved 2015 08 31 Hansen Tony Hardie Ted June 2015 Thaler Dave ed Guidelines and Registration Procedures for URI Schemes doi 10 17487 RFC7595 RFC 7595 Mealling Michael Denenberg Ray eds August 2002 Report from the Joint W3C IETF URI Planning Interest Group Uniform Resource Identifiers URIs URLs and Uniform Resource Names URNs Clarifications and Recommendations doi 10 17487 RFC3305 RFC 3305 Retrieved 2015 09 13 Berners Lee Tim Fielding Roy T Masinter Larry January 2005 Uniform Resource Identifiers URI Generic Syntax doi 10 17487 RFC3986 RFC 3986 Retrieved 2015 08 31 Berners Lee Tim Fielding Roy T Masinter Larry January 2005 Uniform Resource Identifiers URI Generic Syntax section 3 Syntax Components doi 10 17487 RFC3986 RFC 3986 Retrieved 2015 08 31 An Introduction to Multilingual Web Addresses 2008 05 09 Retrieved 2015 01 11 Phillip A 2014 What is Happening with International URLs World Wide Web Consortium Retrieved 2015 01 11 Lawrence Eric 2014 03 06 Browser Arcana IP Literals in URLs docs microsoft com Archived from the original on 2020 06 22 Retrieved 2020 06 22 External linksURL specification at WHATWG Retrieved from https en wikipedia org w index php title URL amp oldid 1127671674, wikipedia, wiki, book, books, library,

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