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42-477: URIs which provide a means of locating and retrieving information resources on a network (either on the Internet or on another private network, such as a computer filesystem or an Intranet ) are Uniform Resource Locators ( URLs ). Therefore, URLs are a subset of URIs, ie. every URL is a URI (and not necessarily the other way around). Other URIs provide only a unique name, without a means of locating or retrieving

84-463: 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 generally not considered to be a URI, because the URI specification bases the decision not only on lexical components, but also on their intended use. A namespace name does not necessarily imply any of

126-462: A "hypertext name" or "document name". Over the next three and a half years, as the World Wide Web's core technologies of HTML , HTTP , and web browsers developed, a need to distinguish a string that provided an address for a resource from a string that merely named a resource emerged. Although not yet formally defined, the term Uniform Resource Locator came to represent the former, and

168-574: A minor update to RFC 2396, allowing URIs to accommodate IPv6 addresses. A number of shortcomings discovered in the two specifications led to a community effort, coordinated by RFC 2396 co-author Roy Fielding , that culminated in the publication of IETF RFC   3986 in January 2005. While obsoleting the prior standard, it did not render the details of existing URL schemes obsolete; RFC 1738 continues to govern such schemes except where otherwise superseded. IETF RFC   2616 for example, refines

210-422: A rate of 120 words a minute The idea of using computers to search for relevant pieces of information was popularized in the article As We May Think by Vannevar Bush in 1945. It would appear that Bush was inspired by patents for a 'statistical machine' – filed by Emanuel Goldberg in the 1920s and 1930s – that searched for documents stored on film. The first description of a computer searching for information

252-512: A scheme component followed by a colon ( : ). A path segment that contains a colon character (e.g., foo:bar ) cannot be used as the first path segment of a relative reference if its path component does not begin with a slash ( / ), as it would be mistaken for a scheme component. Such a path segment must be preceded by a dot path segment (e.g., ./foo:bar ). Web document markup languages frequently use URI references to point to other resources, such as external documents or specific portions of

294-496: A specific edition of the William Shakespeare play Romeo and Juliet . The URN for that edition would be urn:isbn:0-486-27557-4 . However, it gives no information as to where to find a copy of that book. A Uniform Resource Locator (URL) is a URI that specifies the means of acting upon or obtaining the representation of a resource, i.e. specifying both its primary access mechanism and network location. For example,

336-459: 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. A component is empty if it has no characters; the scheme component is always non-empty. The authority component consists of subcomponents : This is represented in a syntax diagram as: [REDACTED] The URI comprises: The scheme- or implementation-specific reserved character + may be used in

378-658: Is a superset of the syntax of all URI schemes. It was first defined in RFC   2396 , published in August 1998, and finalized in RFC   3986 , published in January 2005. A URI is composed from an allowed set of ASCII characters consisting of reserved characters (gen-delims: : , / , ? , # , [ , ] , and @ ; sub-delims: ! , $ , & , ' , ( , ) , * , + , , , ; , and = ), unreserved characters ( uppercase and lowercase letters , decimal digits , - , . , _ , and ~ ), and

420-538: Is a technique by which a command is appended to a URL, usually at the end, after a "?" token . It is commonly used in WebDAV as a mechanism of adding functionality to HTTP . In a versioning system, for example, to add a "checkout" command to a URL, it is written as http://editing.com/resource/file.php?command=checkout . It has the advantage of both being easy for CGI parsers and also acts as an intermediary between HTTP and underlying resource, in this case. In XML ,

462-491: Is a useful but informal concept: a URL is a type of URI that identifies a resource via a representation of its primary access mechanism (e.g., its network "location"), rather than by some other attributes it may have. As such, a URL is simply a URI that happens to point to a resource over a network. However, in non-technical contexts and in software for the World Wide Web, the term "URL" remains widely used. Additionally,

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504-445: Is an entity that is represented by information in a content collection or database . User queries are matched against the database information. However, as opposed to classical SQL queries of a database, in information retrieval the results returned may or may not match the query, so results are typically ranked. This ranking of results is a key difference of information retrieval searching compared to database searching. Depending on

546-548: Is analogous to a person's name, while a URL is analogous to their street address. In other words, a URN identifies an item and a URL provides a method for finding it. Technical publications, especially standards produced by the IETF and by the W3C, normally reflect a view outlined in a W3C Recommendation of 30 July 2001, which acknowledges the precedence of the term URI rather than endorsing any formal subdivision into URL and URN. URL

588-474: Is the science of searching for information in a document, searching for documents themselves, and also searching for the metadata that describes data, and for databases of texts, images or sounds. Automated information retrieval systems are used to reduce what has been called information overload . An IR system is a software system that provides access to books, journals and other documents; it also stores and manages those documents. Web search engines are

630-423: Is the process of assessing how well a system meets the information needs of its users. In general, measurement considers a collection of documents to be searched and a search query. Traditional evaluation metrics, designed for Boolean retrieval or top-k retrieval, include precision and recall . All measures assume a ground truth notion of relevance: every document is known to be either relevant or non-relevant to

672-567: The http scheme. 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 2001, the World Wide Web Consortium's (W3C) Technical Architecture Group (TAG) published a guide to best practices and canonical URIs for publishing multiple versions of a given resource. For example, content might differ by language or by size to adjust for capacity or settings of

714-575: The RFC   1630 attempted to summarize the syntaxes of URL schemes in use at the time. It acknowledged -- but did not standardize —the existence of relative URLs and fragment identifiers. In December 1994, RFC   1738 formally defined relative and absolute URLs, refined the general URL syntax, defined how to resolve relative URLs to absolute form, and better enumerated the URL schemes then in use. The agreed definition and syntax of URNs had to wait until

756-510: The application the data objects may be, for example, text documents, images, audio, mind maps or videos. Often the documents themselves are not kept or stored directly in the IR system, but are instead represented in the system by document surrogates or metadata . Most IR systems compute a numeric score on how well each object in the database matches the query, and rank the objects according to this value. The top ranking objects are then shown to

798-824: The Cranfield collection (several thousand documents). Large-scale retrieval systems, such as the Lockheed Dialog system, came into use early in the 1970s. In 1992, the US Department of Defense along with the National Institute of Standards and Technology (NIST), cosponsored the Text Retrieval Conference (TREC) as part of the TIPSTER text program. The aim of this was to look into the information retrieval community by supplying

840-637: The Semantic Web , which explained the use of content negotiation and the HTTP 303 response code for redirections in more detail. A Uniform Resource Name (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 identifies

882-524: The URL http://example.org/wiki/Main_Page refers to a resource identified as /wiki/Main_Page , whose representation is obtainable via the Hypertext Transfer Protocol ( http: ) from a network host whose domain name is example.org . (In this case, HTTP usually implies it to be in the form of HTML and related code. In practice, that is not necessarily the case, as HTTP allows specifying arbitrary formats in its header.) A URN

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924-426: The allowed set or is being used as a delimiter of, or within, the component. A percent-encoding of an identifying data octet is a sequence of three characters, consisting of the character % followed by the two hexadecimal digits representing that octet's numeric value. The URI generic syntax consists of five components organized hierarchically in order of decreasing significance from left to right: A component

966-483: The basis for namespace names in addition to URI references. Information retrieval Information retrieval ( IR ) in computing and information science is the task of identifying and retrieving information system resources that are relevant to an information need . The information need can be specified in the form of a search query. In the case of document retrieval, queries can be based on full-text or other content-based indexing. Information retrieval

1008-404: The character % . Syntax components and subcomponents are separated by delimiters from the reserved characters (only from generic reserved characters for components) and define identifying data represented as unreserved characters, reserved characters that do not act as delimiters in the component and subcomponent respectively, and percent-encodings when the corresponding character is outside

1050-500: The debate over defining URLs and URNs, it became evident that the concepts embodied by the two terms were merely aspects of the fundamental, overarching, notion of resource identification . In June 1994, the IETF published Berners-Lee's first Request for Comments that acknowledged the existence of URLs and URNs. Most importantly, it defined a formal syntax for Universal Resource Identifiers (i.e. URL-like strings whose precise syntaxes and semantics depended on their schemes). In addition,

1092-447: The device used to access that content. In August 2002, IETF RFC   3305 pointed out that the term "URL" had, despite widespread public use, faded into near obsolescence, and serves only as a reminder that some URIs act as addresses by having schemes implying network accessibility, regardless of any such actual use. As URI-based standards such as Resource Description Framework make evident, resource identification need not suggest

1134-425: The documents are typically transformed into a suitable representation. Each retrieval strategy incorporates a specific model for its document representation purposes. The picture on the right illustrates the relationship of some common models. In the picture, the models are categorized according to two dimensions: the mathematical basis and the properties of the model. The evaluation of an information retrieval system'

1176-581: The infrastructure that was needed for evaluation of text retrieval methodologies on a very large text collection. This catalyzed research on methods that scale to huge corpora. The introduction of web search engines has boosted the need for very large scale retrieval systems even further. Areas where information retrieval techniques are employed include (the entries are in alphabetical order within each category): Methods/Techniques in which information retrieval techniques are employed include: In order to effectively retrieve relevant documents by IR strategies,

1218-504: The more contentious Uniform Resource Name came to represent the latter. In July 1992 Berners-Lee's report on the Internet Engineering Task Force (IETF) "UDI (Universal Document Identifiers) BOF " mentions URLs (as Uniform Resource Locators), URNs (originally, as Unique Resource Numbers), and the need to charter a new working group. In November 1992 the IETF "URI Working Group" met for the first time. During

1260-422: The most visible IR applications. An information retrieval process begins when a user enters a query into the system. Queries are formal statements of information needs, for example search strings in web search engines. In information retrieval, a query does not uniquely identify a single object in the collection. Instead, several objects may match the query, perhaps with different degrees of relevance . An object

1302-473: The path, query and fragment, and the generic reserved character ? may be used in the query and fragment. The following figure displays example URIs and their component parts. DOIs ( digital object identifiers ) fit within the Handle System and fit within the URI system, as facilitated by appropriate syntax . A URI reference is either a URI or a relative reference when it does not begin with

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1344-516: The publication of IETF RFC   2141 in May 1997. The publication of IETF RFC   2396 in August 1998 saw the URI syntax become a separate 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 from "Universal" to "Uniform." In December 1999, RFC   2732 provided

1386-401: The resource or information about it; these are Uniform Resource Names (URNs). The web technologies that use URIs are not limited to web browsers . URIs and URLs have a shared history. In 1990, 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

1428-548: 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 for practical uses, a distinction which has caused confusion as to how to distinguish the two. The TAG published an e-mail in 2005 with a solution of the problem, which became known as the httpRange-14 resolution . The W3C subsequently published an Interest Group Note titled Cool URIs for

1470-400: The same logical document: Resolving a URI reference against a base URI results in a target URI . This implies that the base URI exists and is an absolute URI (a URI with no fragment component). The base URI can be obtained, in order of precedence, from: Within a representation with a well defined base URI of a relative reference is resolved to its target URI as follows: URL munging

1512-430: The scheme http is generally used for interacting with web resources using HTTP, but the scheme file has no protocol. A URI has a scheme that refers to a specification for assigning identifiers within that scheme. As such, the URI syntax is a federated and extensible naming system wherein each scheme's specification may further restrict the syntax and semantics of identifiers using that scheme. The URI generic syntax

1554-425: The scheme, userinfo, host, path, query, and fragment, and the scheme- or implementation-specific reserved characters ! , $ , & , ' , ( , ) , * , , , ; , and = may be used in the userinfo, host, path, query, and fragment. Additionally, the generic reserved character : may be used in the userinfo, path, query and fragment, the generic reserved characters @ and / may be used in

1596-467: The semantics of URI schemes; for example, a namespace name beginning with http: may have no connotation to the use of the HTTP . Originally, the namespace name could match the syntax of any non-empty URI reference, but the use of relative URI references was deprecated by the W3C. A separate W3C specification for namespaces in XML 1.1 permits Internationalized Resource Identifier (IRI) references to serve as

1638-483: The term "web address" (which has no formal definition) often occurs in non-technical publications as a synonym for a URI that uses the http or https schemes. Such assumptions can lead to confusion, for example, in the case of XML namespaces that have a visual similarity to resolvable URIs . Specifications produced by the WHATWG prefer URL over URI , and so newer HTML5 APIs use URL over URI . Standardize on

1680-421: The term URL. URI and IRI [Internationalized Resource Identifier] are just confusing. In practice a single algorithm is used for both so keeping them distinct is not helping anyone. URL also easily wins the search result popularity contest. While most URI schemes were originally designed to be used with a particular protocol , and often have the same name, they are semantically different from protocols. For example,

1722-482: The user. The process may then be iterated if the user wishes to refine the query. there is ... a machine called the Univac ... whereby letters and figures are coded as a pattern of magnetic spots on a long steel tape. By this means the text of a document, preceded by its subject code symbol, can be recorded ... the machine ... automatically selects and types out those references which have been coded in any desired way at

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1764-494: Was described by Holmstrom in 1948, detailing an early mention of the Univac computer. Automated information retrieval systems were introduced in the 1950s: one even featured in the 1957 romantic comedy, Desk Set . In the 1960s, the first large information retrieval research group was formed by Gerard Salton at Cornell. By the 1970s several different retrieval techniques had been shown to perform well on small text corpora such as

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