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A Uniform Resource Identifier (URI), is a compact string of characters used to identify or name a resource. The main purpose of this identification is to enable interaction with representations of the resource over a network, typically the World Wide Web, using specific protocols. URIs are defined in schemes defining a specific syntax and associated protocols. In various branches of mathematics and computer science, strings are sequences of various simple objects (symbols, tokens, characters, etc. ...
Identifiers (IDs) are lexical tokens that name entities. ...
A name is a label for a person, thing, place, product (as in a brand name) and even an idea or concept, normally used to distinguish one from another. ...
The term resource is a foundational term in World Wide Web architecture because it is the root of Uniform Resource Identifiers, also known as URIs and URLs. ...
WWWs historical logo designed by Robert Cailliau The World Wide Web (WWW or simply the Web) is a system of interlinked, hypertext documents that runs over the Internet. ...
For other senses of this word, see protocol. ...
For other uses, see Syntax (disambiguation). ...
Relationship to URL and URN
The contemporary point of view among the working group that oversees URIs is that the terms URL and URN are context-dependent aspects of URIs, and rarely need to be distinguished.[1] The term URI is more general than URL or URN and may include them as special cases. Wikipedia does not have an article with this exact name. ...
Uniform Resource Locator (URL) is a technical, Web-related term used in two distinct meanings: in popular usage, it is a widespread synonym for Uniform Resource Identifier (URI) — many popular and technical texts will use the term URL when referring to URI; strictly, the idea of a uniform syntax for...
A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) that uses the urn scheme, and does not imply availability of the identified resource. ...
In technical publications, especially standards produced by the IETF and the W3C, the term URL has long been deprecated, as it is rarely necessary to distinguish between URLs and URIs. However, in nontechnical contexts and in software for the World Wide Web, the term URL remains ubiquitous. Additionally, the term web address, which has no formal definition, is often used in nontechnical publications as a synonym for URL or URI, although it generally refers only to 'http' and 'https' URIs. The Internet Engineering Task Force (IETF) develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standard bodies; and dealing in particular with standards of the TCP/IP and Internet protocol suite. ...
The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web (W3). ...
Syntax The URI syntax is essentially a URI scheme name like "http", "ftp", "mailto", "urn", "tel", "rtsp", etc., followed by a colon character, and then a scheme-specific part. The syntax and semantics of the scheme-specific part are determined by the specifications that govern the schemes, although the URI syntax does force all schemes to adhere to a certain generic syntax that, among other things, reserves certain characters for special purposes, without always saying what those purposes are. The URI syntax also enforces restrictions on the scheme-specific part, in order to, for example, provide for a degree of consistency when the part has a hierarchical structure. Percent-encoding is an often misunderstood aspect of URI syntax. A URI scheme is the top level of the URI (Uniform Resource Identifier) naming structure. ...
Hypertext Transfer Protocol (HTTP) is a method used to transfer or convey information on the World Wide Web. ...
FTP or File Transfer Protocol is used to transfer data from one computer to another over the Internet, or through a network. ...
Wikipedia does not yet have an article with this exact name. ...
A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) that uses the urn scheme, and does not imply availability of the identified resource. ...
The Real Time Streaming Protocol (RTSP), developed by the IETF and published in 1998 as RFC 2326, is a protocol for use in streaming media systems which allows a client to remotely control a streaming media server, issuing VCR-like commands such as play and pause, and allowing time-based...
The colon (:) is a punctuation mark, visually consisting of two equally sized dots centered on the same vertical line. ...
Semantics (Greek semantikos, giving signs, significant, symptomatic, from sema, sign) refers to the aspects of meaning that are expressed in a language, code, or other form of representation. ...
Percent-encoding, also known as URL encoding, is a mechanism for encoding information in a Uniform Resource Identifier (URI) under certain circumstances. ...
- See also URI generic syntax
A URI scheme is the top level of the URI (Uniform Resource Identifier) naming structure. ...
History
Naming, addressing, and identifying resources URIs and URLs have a shared history. The idea of a URL — a short string representing a resource that is the target of a hyperlink — was implicitly introduced in late 1990 in Tim Berners-Lee's proposals for HyperText [1]. At the time, it was called a hypertext name or document name[2] A hyperlink (often referred to as simply a link), is a reference or navigation element in a document to another section of the same document, another document, or a specified section of another document, that automatically brings the referred information to the user when the navigation element is selected by...
1990 (MCMXC) was a common year starting on Monday of the Gregorian calendar. ...
Sir Tim Berners-Lee Sir Tim (Timothy John) Berners-Lee, KBE (TimBL or TBL) (b. ...
In computing, hypertext is a user interface paradigm for displaying documents which, according to an early definition (Nelson 1970), branch or perform on request. ...
Over the next three-and-a-half years, as the World Wide Web's core technologies of HTML (the HyperText Markup Language), HTTP, and Web browsers were developed, a need to distinguish between strings that provide an address for resources and those that merely name resources emerged. Although not yet formally defined, the term Uniform Resource Locator came to represent strings used for the former purpose, and the more contentious Uniform Resource Name came to represent strings used for the latter purpose. HTML, short for HyperText Markup Language, is the predominant markup language for the creation of web pages. ...
A specialized markup language using SGML is used to write the electronic version of the Oxford English Dictionary. ...
HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ...
An example of a web browser (Mozilla Firefox), displaying the English Wikipedia main page. ...
During the debate over how to best define URLs and URNs, it became evident that the two concepts embodied by the terms were merely aspects of the fundamental, overarching notion of resource identification. So, in June 1994, the IETF published Berners-Lee's RFC 1630: the first RFC that (in its non-normative text) acknowledged 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 were dependent upon their scheme. In addition, this RFC attempted to summarize the syntax of URL schemes that were in use at the time. It also acknowledged, but did not standardize, the existence of relative URLs and fragment identifiers. 1994 (MCMXCIV) was a common year starting on Saturday of the Gregorian calendar, and was designated as the International Year of the Family and the International Year of the Sport and the Olympic Ideal by United Nations. ...
The Internet Engineering Task Force (IETF) is charged with developing and promoting Internet standards. ...
In internetworking and computer network engineering, Request for Comments (RFC) documents are a series of memoranda encompassing new research, innovations, and methodologies applicable to Internet technologies. ...
A fragment identifier is a short string of characters that refers to a resource that is subordinate to another, primary resource. ...
Refinement of specifications In December 1994, RFC 1738 was published in order to formally define relative and absolute URLs, refine the general URL syntax, define how relative URLs were to be resolved to absolute form, and better enumerate the URL schemes that were in use at the time. The definition and syntax of URNs was not settled upon until the publication of RFC 2141 in May 1997. 1997 (MCMXCVII) was a common year starting on Wednesday of the Gregorian calendar. ...
With the publication of RFC 2396 in 1998, the URI syntax became a separate specification, and most parts of RFCs 1630 and 1738 became obsolete. In the new RFC, the "U" in "URI" was changed to represent "Uniform" rather than "Universal", and all parts of RFCs 1630 and 1738 relating to URIs and URLs in general were revised and expanded. Only those portions of RFC 1738 that summarized existing URL schemes were not rendered obsolete by RFC 2396. 1998 (MCMXCVIII) was a common year starting on Thursday of the Gregorian calendar, and was designated the International Year of the Ocean [1]. // Coated in ice, power and telephone lines sag and often break, resulting in power outages. ...
In December 1999, RFC 2732 provided a minor update to RFC 2396, allowing URIs to accommodate IPv6 addresses. Some time later, a number of shortcomings discovered in the two specifications led to the development of a number of draft revisions under the title rfc2396bis. This community effort, coordinated by RFC 2396 co-author Roy Fielding, culminated in the publication of RFC 3986 in January 2005. This RFC is the current version of the URI syntax recommended for use on the Internet, and it renders RFC 2396 obsolete. It does not, however, render the details of existing URL schemes obsolete; those are still governed by RFC 1738, except where otherwise superseded — RFC 2616 for example, refines the "http" scheme. The content of RFC 3986 was simultaneously published by the IETF as the full standard STD 66, reflecting the establishment of the URI generic syntax as an official Internet protocol. 1999 (MCMXCIX) was a common year starting on Friday, and was designated the International Year of Older Persons by the United Nations. ...
Internet Protocol version 6 (IPv6) is a network layer protocol for packet-switched internetworks. ...
Roy T. Fielding (born 1965) is one of the principal authors of the HTTP specification and a frequently-cited authority on computer network architecture. ...
2005 (MMV) was a common year starting on Saturday of the Gregorian calendar. ...
In August 2002, RFC 3305 pointed out that the term URL has, despite its ubiquity in the vernacular of the Internet-aware public at large, faded into near-obsolescence. It now serves only as a reminder that some URIs act as addresses because they have schemes that imply some kind of network accessibility, regardless of whether they are actually being used for that purpose. As URI-based standards such as Resource Description Framework make evident, resource identification need not be coupled with the retrieval of resource representations over the Internet, nor does it need to be associated with network-bound resources at all. For album titles with the same name, see 2002 (album). ...
Resource Description Framework (RDF) is a family of World Wide Web Consortium (W3C) specifications originally designed as a metadata model using XML but which has come to be used as a general method of modeling knowledge, through a variety of syntax formats (XML and non-XML). ...
URI reference A URI reference is another type of string that represents a URI, and, in turn, the resource identified by that URI. The distinction between a URI and a URI reference is not often maintained in informal usage, but protocol documents should not allow for ambiguity.
A URI reference may take the form of a full URI, or just the scheme-specific portion of one, or even some trailing component thereof—even the empty string. An optional fragment identifier, preceded by "#", may be present at the end of a URI reference. The part of the reference before the "#" indirectly identifies a resource, and the fragment identifier identifies some portion of that resource.
In order to derive a URI from a URI reference, the URI reference is converted to "absolute" form by merging it with an absolute "base" URI, according to a fixed algorithm. The URI reference is considered to be relative to the base URI, although if the reference itself is absolute, then the base is irrelevant. The base URI is typically the URI that identifies the document containing the URI reference, although this can be overridden by declarations made within the document or as part of an external data transmission protocol. If a identifier is present in the base URI, it is ignored during the merging process. If a fragment identifier is present in the URI reference, it is preserved during the merging process.
In web document markup languages, URI references are frequently used in places where there is a need to point to other resources, such as external documents or specific portions of the same logical document.
Uses of URI references in markup languages - In HTML, the value of the
src attribute of the img element is a URI reference, as is the value of the href attribute of the a or link element. - In XML, the system identifier appearing after the
SYSTEM keyword in a DTD is a fragmentless URI reference; - In XSLT, the value of the
href attribute of the xsl:import element/instruction is a URI reference, as is the first argument to the document() function. HTML, short for HyperText Markup Language, is the predominant markup language for the creation of web pages. ...
The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language that supports a wide variety of applications. ...
A system identifier is a document processing construct introduced in the HyTime markup language as a supplement to SGML. It was subsequently incorporated into the HTML and XML markup languages. ...
Document Type Definition (DTD), defined slightly differently within the XML and SGML specifications, is one of several SGML and XML schema languages, and is also the term used to describe a document or portion thereof that is authored in the DTD language. ...
...
Examples of absolute URIs - http://somehost/absolute/URI/with/absolute/path/to/resource.txt
- ftp://somehost/resource.txt
- urn:issn:1535-
ISSN, or International Standard Serial Number, is the unique eight-digit number applied to a periodical publication including electronic serials. ...
Examples of URI references - http://example/resource.txt#frag01
- http://somehost/absolute/URI/with/absolute/path/to/resource.txt
- /relative/URI/with/absolute/path/to/resource.txt
- relative/path/to/resource.txt
- ../../../resource.txt
- resource.txt
- /resource.txt#frag01
- #frag01
- (empty string)
URI resolution To "resolve" a URI means either to convert a relative URI reference to absolute form, or to dereference a URI or URI reference by attempting to obtain a representation of the resource that it identifies. The "resolver" component in document processing software generally provides both services.
A URI reference may be considered to be a same-document reference: a reference to the document containing the URI reference itself. Document processing software is encouraged to use its current representation of the document to satisfy the resolution of a same-document reference; a new representation should not be fetched. This is only a recommendation, and document processing software is free to use other mechanisms to determine whether obtaining a new representation is warranted.
According to the current URI specification, RFC 3986, a URI reference is a same-document reference if, when resolved to absolute form, it is identical to the base URI that is in effect for the reference. Typically, the base URI is the URI of the document containing the reference. XSLT 1.0, for example, has a document() function that, in effect, implements this functionality. RFC 3986 also formally defines URI equivalence, which can be used in order to determine that a URI reference, while not identical to the base URI, still represents the same resource and thus can be considered to be a same-document reference.
Same-document references were determined differently according to RFC 2396, which was made obsolete by RFC 3986 but is still used as the basis of many specifications and implementations. According to this specification, a URI reference is a same-document reference if it is an empty string or consists of only the "#" character followed by an optional fragment.
Examples of relative URIs - /relative/URI/with/absolute/path/to/resource.txt
- relative/path/to/resource.txt
- ../../../resource.txt
- resource.txt
Relation to XML namespaces XML has a concept of a namespace, an abstract domain to which a collection of element and attribute names can be assigned. An XML namespace is identified by a character string, the namespace name, which must adhere to the generic URI syntax. However, the namespace name is not considered to be a URI because the "URI-ness" of strings is, according to the URI specification, based on how they are intended to be used, not just their lexical components. A namespace name also does not necessarily imply any of the semantics of URI schemes; a namespace name beginning with "http:", for example, likely has nothing to do with the HTTP protocol. There has been much debate about this among XML professionals on the xml-dev electronic mailing list; some feel that a namespace name could be a URI, since the collection of names comprising a particular namespace could be considered to be a resource that is being identified, and since the Namespaces in XML specification says that the namespace name is a URI reference. The consensus seems to be, though, that a namespace name is just a string that happens to look like a URI, nothing more. The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language that supports a wide variety of applications. ...
An XML namespace is a W3C standard for providing uniquely named elements and attributes in an XML instance. ...
HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ...
Electronic mailing lists are a special usage of e-mail that allows for widespread distribution of information to many Internet users. ...
Initially, the namespace name was allowed to match the syntax of any non-empty URI reference, but the use of relative URI references was later deprecated by an erratum to the Namespaces In XML Recommendation. A separate specification was issued for namespaces for XML 1.1, and allows IRI references, not just URI references, to be used as the basis for namespace names. The introduction of this article does not provide enough context for readers unfamiliar with the subject. ...
In order to mitigate the confusion that began to arise among newcomers to XML from the use of URIs (particularly HTTP URLs) for namespaces, a descriptive language called RDDL was developed. An RDDL document can provide machine- and human-readable information about a particular namespace and about the XML documents that use it. XML document authors were encouraged to put RDDL documents in locations such that if a namespace name in their document was somehow dereferenced, then an RDDL document would be obtained, thus satisfying the desire among many developers for a namespace name to point to a network-accessible resource. In computing, Resource Directory Description Language (RDDL) is an extension of XHTML Basic 1. ...
See also Originally intended to share data between a few universities and government agencies, the Internet today allows connectivity from anywhere on earth and beyond—even ships at sea and in outer space. ...
The introduction of this article does not provide enough context for readers unfamiliar with the subject. ...
In many programming languages, a namespace is a context for identifiers. ...
Percent-encoding, also known as URL encoding, is a mechanism for encoding information in a Uniform Resource Identifier (URI) under certain circumstances. ...
On the Internet, a persistent uniform resource locator (PURL) is a uniform resource locator (URL) (i. ...
A URI scheme is the top level of the URI (Uniform Resource Identifier) naming structure. ...
Uniform Resource Locator (URL) is a technical, Web-related term used in two distinct meanings: in popular usage, it is a widespread synonym for Uniform Resource Identifier (URI) — many popular and technical texts will use the term URL when referring to URI; strictly, the idea of a uniform syntax for...
A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) that uses the urn scheme, and does not imply availability of the identified resource. ...
A website (or Web site) is a collection of web pages, images, videos and other digital assets and hosted on a particular domain or subdomain on the World Wide Web. ...
XRI (eXtensible Resource Identifier) is a scheme and resolution protocol for abstract identifiers compatible with Uniform Resource Identifiers and Internationalized Resource Identifiers, developed by the XRI Technical Committee at OASIS. The goal of XRIs is to provide a universal format for identifiers that are domain-, location-, application-, and transport-independent...
References - ^ RFC 3305 and W3C Note: URIs, URLs, and URNs: Clarifications and Recommendations 1.0 (the same content, published by different authorities).
External links - RFC 3986 / STD 66 (2005) – the current generic URI syntax specification
- RFC 2396 (1998) and RFC 2732 (1999) – obsolete, but widely implemented, version of the generic URI syntax
- RFC 1808 (1995) – obsolete companion to RFC 1738 covering relative URL processing
- RFC 1738 (1994) – mostly obsolete definition of URL schemes and generic URI syntax
- RFC 1630 (1994) – the first generic URI syntax specification; first acknowledgment of URLs in an Internet standard
- IANA-maintained registry of URI Schemes
- URI Working Group – coordination center for development of URI standards
- Architecture of the World Wide Web, Volume One, §2: Identification – by W3C
- Example of discussion about names and addresses
- Identifying, locating, and naming things on the Web – by D.Connolly
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