Friday, May 26, 2017

Uniform Resource Locators usually start with http://www. etc.

 a Uniform resource locator is also called a URL which is used for computers to navigate on the world wide web

for example, https://en.wikipedia.org/wiki/URL   is literally the URL or  uniform resource locator for this article when it is located at wikipedia.com

So, if you look up on your computer often it displays this on every page you are on. I make sure it does on my computer near the top of each screen. Then if I can't find the word button I can always give you the reader the URL for the site so you can either copy and paste it to find the source or you can take the name of the article (if it is a large newspaper especially or magazine) and easily find the article online if it is there to find where the source of the quote is from. In other words if you can't see the URL on most computers there is a way to force your computer to display this in most countries so you can always see the URL of every site and page you visit online.

begin quote from:
Uniform Resource Locators

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URL

From Wikipedia, the free encyclopedia
  (Redirected from Uniform Resource Locator)
For other uses, see URL (disambiguation).
A Uniform Resource Locator (URL), colloquially termed 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] although many people use the two terms interchangeably.[3] 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.[4][3] Thus http://www.example.com is a URL, while www.example.com is not.[5] 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).

Contents

History

Uniform Resource Locators were defined in Request for Comments (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),[6] 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 file names. 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]

Syntax

Main article: Uniform resource identifier § Syntax
Every HTTP URL conforms to the syntax of a generic URI. A generic URI is of the form:
 scheme:[//[user[:password]@]host[:port]][/path][?query][#fragment]
It comprises:
  • 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. URI schemes should be registered with the Internet Assigned Numbers Authority (IANA), although non-registered schemes are used in practice.[a]
  • Two slashes (//): This is required by some schemes and not required by some others. When the authority component (explained below) is absent, the path component cannot begin with two slashes.[12]
  • An authority part, comprising:
  • 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.[15] 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)
Query delimiter Example
Ampersand (&) key1=value1&key2=value2
Semicolon (;)[c][incomplete short citation] 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 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 will 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.[17][18]
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.[19]
The URL path name can also be specified by the user in the local alphabet. If not already encoded, it is converted to Unicode, and any characters not part of the basic URL character set are converted to English letters 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.[17]

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, either HTTP or HTTPS.[20][21]

See also

Notes


  • 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.[11]
    1. Historic RFC 1866 (obsoleted by RFC 2854) encourages CGI authors to support ';' in addition to '&'.[16]

    Citations


    1. Steven M. Schafer (2011). HTML, XHTML, and CSS Bible. John Wiley & Sons. p. 124. Retrieved 12 October 2015.

    References

    External links

  • 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.[14]
  • W3C (2009).
  • RFC 3986 (2005).
  • Joint W3C/IETF URI Planning Interest Group (2002).
  • RFC 2396 (1998).
  • Miessler, Daniel. "The Difference Between URLs and URIs".
  • W3C (1994).
  • IETF (1992).
  • Berners-Lee (1994).
  • Berners-Lee (2000).
  • BBC News (2009).
  • IETF (2015).
  • RFC 3986 (2005), §3.
  • RFC 3986 (2005), §3.2.2.
  • Lawrence (2014).
  • RFC 2396 (1998), §3.3.
  • RFC 1866 (1995), §8.2.1.
  • W3C (2008).
  • W3C (2014).
  • IANA (2003).
  • J. D. Glaser (2013). Secure Development for Mobile Apps: How to Design and Code Secure Mobile Applications with PHP and JavaScript. CRC Press. p. 193. Retrieved 12 October 2015.
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