Source: https://www.jdvorak.eu/uniform-resource-identifier/
Timestamp: 2019-04-23 06:12:29+00:00

Document:
Such identification enables interaction with representations of the resource over a network, typically the World Wide Web , using specific protocols . Schemes specifying a concrete syntax and associated protocols define each URI. The most common form of URI is the Uniform Resource Locator ( URL ), which is frequently referred to informally as a web address. More rarely seen in use is the Uniform Resource Name (URN) , which was designed to complement URLs by providing a mechanism for the identification of resources in particular namespaces .
A Uniform Resource Name (URN) may be compared to a person’s name, while a Uniform Resource Locator (URL) may be compared to their street address. In other words, a URN identifies an item and a URL provides a method for finding it.
A URL is a URI which, in addition to identifying a web resource, specifies the means of acting upon or obtaining the representation of it, ie specifying both its primary access mechanism and network location. For example, the URL http://example.org/wiki/Main_Page refers to a resource identified as / wiki / Main_Page whose representation, in the form of HTML and related code, is obtainable via the Hypertext Transfer Protocol ( http 🙂 from a network host where domain name is example.org .
A URN is a URI that identifies a resource by name in a particular namespace. A URN may be used to talk about a resource without implying its location or how to access it. For example, in the International Standard Book Number (ISBN) system, ISBN 0-486-27557-4 identified a specific edition of Shakespeare ‘s play Romeo and Juliet . The URN for that edition would be urn: isbn: 0-486-27557-4 . To gain access to the book, it is needed, for which a URL would have to be specified.
Technical publications, Especially standard produced by the IETF and by the W3C , Normally Reflect view Outlined in a W3C Recommendation of 2001, qui acknowledges the precedence of the term URI Rather than endorsing Any formal subdivision into URL and URN.
However, in non-technical contexts and in software for the World Wide Web, the term URL remains widely used. Additionally, the term web address (which has no formal definition) often occurs in non-technical publications as a synonym for a URI that uses the scheme http or https . Such assumptions can lead to confusion, for example in the case of XML namespaces, which have a visual similarity to resolvable URIs .
While most URI schemes were originally designed to be used with a particular protocol , they are often semantically different from protocols. For example, the scheme http is Generally used for interacting with web resources using HTTP, the scheme aims file Has No protocol.
A path , which contains data, usually organized in hierarchical form, which appears as a sequence of segments separated by slashes. Such a sequence May resemble gold map exactly to a file system path , goal does not always Imply a relationship to one.  The path must begin with a single slash ( /) if an authority is present, and may also be, but not begin with a double slash. The path is always defined, but the defined path may be empty (zero length), therefore no trailing slash.
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 identification providing a direction to a secondary resource, such 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 idattribute of a specific element.
Strings of data bytes within a URI are represented as characters. Permitted characters Within a URI are the ASCII characters for the lowercase and uppercase letters of the modern English alphabet , the Arabic numerals , hyphen, period , underscore , and tilde .  Octets represented by any other character must be percent-encoded .
The following figure displays the example URIs and their component parts.
In HTML , the value of the srcattribute of the imgelement Provides a URI reference, as does the value of the hrefattribute of the agold linkelement.
In XML , the system identifier appears after the SYSTEMkeyword in a DTD is a fragmentless URI reference.
In XSLT , the value of the hrefattribute of the xsl:importelement / instruction is a URI reference; likewise the first argument to the document()function.
To resolve a URI means to convert a relative URI reference to absolute form, or to refer to URI or URI reference, by attempting to obtain a representation of the resource that it identifies.
URIs and URLs have a shared history. In 1994 Tim Berners-Lee’s Proposals for hypertext  implicitly Introduced the idea of a URL as a short string Representing a resource That is the target of a hyperlink . At the time, people referred to it as “hypertext name”  or “document name”.
Over the next three and a half years, the World Wide Web’s core technologies of HTML, HTTP, and web browsers developed, a need to distinguish a string that provides an address for a resource. ALTHOUGH not yet Formally defined, the term Uniform Resource Locator cam to Represent the form, and the more contentious Uniform Resource Name cam to Represent the lath.
During the debate on defining URLs and URNs, it has become clear that the two concepts are merely overarching notion of resource identification . In June 1994, the IETF published Berners-Lee’s RFC 1630: the first Request for Comments that the existence of URLs and URNs, and, more importantly, defined a formal syntax for Universal Resource Identifiers (URL-like strings whose precise syntax and semantics depended on their schemes. In addition, this RFC attempted to summarize the syntaxes of URL schemes in use at the time. It also acknowledged, but did not standardize, the existence of relative URLs and fragment identifiers.
The publication of RFC 2396 in August 1998 saw the syntax of a particular specification  and most of the parts of RFCs 1630 and 1738 relating to URIs and URLs in general were revised and expanded by the IETF . The new RFC changed the meaning of “U” in “URI” to “Uniform” from “Universal”.
In December 1999, RFC 2732 provided a minor update to RFC 2396, allowing URIs to accommodate IPv6 addresses. A co-author Roy Fielding , co-authored by RFC 2396 , which culminated in the publication of RFC 3986 in January 2005. While obsoleting the prior standard, it did not render the details existing URL schemes obsolete; RFC 1738 continues to govern such schemes except where superseded. RFC 2616 for example, refines the httpscheme. Simultaneously, the IETF published the content of RFC 3986 as the full standard STD 66, reflecting the establishment of the URI generic syntax as an official Internet protocol.
In August 2002, RFC 3305 pointed out that the term “URL” had, rather, made it possible to remem- ber that some URIs act as addresses by having schemes implying network accessibility, regardless of such actuality. use. As URI-based standards such as Resource Description Framework make it obvious, resource identification need not suggest the retrieval of resource representations over the Internet, nor need they imply network-based resources at all.
The Semantic Web uses the HTTP URI scheme to identify both documents and concepts in the real world, a distinction which has caused confusion as to how to distinguish the two. The TAG published an e-mail in 2005 on how to solve the problem, which became known as the httpRange-14 resolution .  The W3C subsequently published an Interest Group Note titled Cool URIs for the Semantic Web ,  qui Explained the use of happy negotiation and the HTTP 303 response code for redirects in more detail.
In XML , a namespace is an abstract domain to which a collection of element and attribute names can be assigned. The namespace name is a character string which must adhere to the generic URI syntax.  However, the name is not considered to be URI,  because the URI specification bases the decision not only on the lexical components, but also on their intended use. A namespace name does not necessarily imply any of the semantics of URI schemes; for example, a namespace name beginning with http: may have no connotation to the use of the HTTP .
Jump up^ A report published in 2002 by W3C / IETF working group to normalize the divergent views held by the IETF and W3C over the relationship between the various ‘UR *’ terms and standards. While not published as a full standard by any organization, it has become the basis for the above common understanding and has many standards since then.
Jump up^ W3C / IETF Joint URI Planning Interest Group (2001).
Jump up^ W3C / IETF Joint URI Planning Interest Group (2002).
^ Jump up to:a b RFC 2396 (1998) .
Jump up^ RFC 3986 (2005).
Jump up^ RFC 3986 (2005), §3.
^ Jump up to:a b RFC 3986 (2005) , §3.2.2.
Jump up^ RFC 2396 (1998), §3.3.
Jump up^ RFC 1866 (1995), §8.2.1.
Jump up^ RFC 3986 (2005), §2.
Jump up^ RFC 3986 (2005), §2.2.
^ Jump up to:a b RFC 3986 (2005) , § 3.3.
Jump up^ RFC 3986 (2005), §3.4.
Jump up^ RFC 3986 (2005), §4.1.
Jump up^ RFC 3986 (2005), §4.2.
^ Jump up to:a b RFC 3986 (2005) , § 5.1.
Jump up^ RFC 3986 (2005), §5.2.2.
^ Jump up to:a b c RFC 3986 (2005) , § 4.4.
Fielding, Roy T. (18 June 2005). “[httpRange-14] Resolved” . Retrieved 24 July 2009 .
Harold, Elliotte Rusty (2004). XML 1.1 Bible (Third ed.). Wiley Publishing . p. 291. ISBN 0-7645-4986-3 .
Joint W3C / IETF URI Planning Interest Group (21 September 2001). “URIs, URLs, and URNs: ​​Clarifications and Recommendations 1.0” . Retrieved 2009-07-27 .
Mealling, M .; Denenberg, R., 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” . World Wide Web Consortium . Retrieved 13 September 2015 .
Hansen, T .; Hardie, T. (June 2015). Thaler, D., ed. “Guidelines and Registration Procedures for URI Schemes” . Internet Engineering Task Force . ISSN 2070-1721 .
Morrison, Michael (2006). “Hour 5: Putting Namespaces to Use “. Sams Teach Yourself XML . Sams Publishing . p. 91.
Palmer, Sean B. (2001). “The Early History of HTML” . Retrieved 2009-04-30 .
URI Planning Interest Group, W3C / IETF (21 September 2001). “URIs, URLs, and URNs: ​​Clarifications and Recommendations 1.0” . Retrieved 2009-07-27 .
“W3 Naming Schemes” . World Wide Web Consortium . 1992 . Retrieved 2009-07-24 .
“On Linking Alternative Representations To Enable Discovery And Publishing” . World Wide Web Consortium . 2006  . Retrieved 2012-04-03 .
Bray, Tim ; Hollander, Dave; Layman, Andrew; Tobin, Richard, eds. (August 16, 2006) “Namespaces in XML 1.1 (Second Edition)” . World Wide Web Consortium . 2.2 Use of URIs as Namespace Names . Retrieved 31 August2015 .
Ayers, Danny; Völkel, Max (3 December 2008). Sauermann, Leo; Cyganiak, Richard, eds. “Cool URIs for the Semantic Web” . World Wide Web Consortium . Retrieved 2012-04-03 .
Bray, Tim ; Hollander, Dave; Layman, Andrew; Tobin, Richard; Thompson, Henry S., eds. (December 8, 2009) “Namespaces in XML 1.0 (Third Edition)” . World Wide Web Consortium . 2.2 Use of URIs as Namespace Names . Retrieved 31 August 2015 .
Berners-Lee, Tim ; Connolly, Dan (November 1995). “Hypertext Markup Language – 2.0” . Internet Engineering Task Force . Retrieved 13 September2015 .
Berners-Lee, Tim ; Fielding, Roy ; Masinter, Larry (August 1998). “Uniform Resource Identifiers (URI): Generic Syntax” . Internet Engineering Task Force . Retrieved 31 August 2015 .
Berners-Lee, Tim ; Fielding, Roy ; Masinter, Larry (January 2005). “Uniform Resource Identifiers (URI): Generic Syntax” . Internet Engineering Task Force . Retrieved 31 August 2015 .
Lawrence, Eric (March 6, 2014). “Arcana Browser: IP Literals in URLs” . IEInternals . Microsoft . Retrieved 2016-04-25 .

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