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The concept of '''Resource''' is primitive in the [[World Wide Web|Web]] architecture, and is used in the definition of its fundamental elements. The term was first introduced to refer to targets of [[Uniform Resource Locator | Uniform Resource Locators]] (URLs), but its definition has been further extended to include the [[referent]] of any [[Uniform Resource Identifier]] (RFC 3986), or [[Internationalized Resource Identifier ]] (RFC 3987). In the [[Semantic Web]], abstract resources and their semantic properties are described using the family of languages based on [[Resource Description Framework]] (RDF).
== History ==
In the early specifications of the Web (1990-1994), the term "resource" is barely used at all. The Web is designed as a network of more or less static addressable objects, basically files and documents, linked together in the form of an hypertext. The objects are considered insofar as they can be addressed and handled through a specific protocol, Web documents are accessed and browsed using [[HTTP]] protocol, files are exchanged using [[File transfer protocol|file transfer protocol]], etc.
The first systematic use of the term resource was introduced in June 1994 by RFC 1630. In this document is defined the generic notion of [[Universal Resource Identifier]] (URI), with its two variants [[ Uniform Resource Locator | Universal Resource Locator]] (URL) and [[ Uniform Resource Name | Universal Resource Name]] (URN). A resource is implicitly defined as something which can be identified, the identification deserving two distinct purposes, naming and addressing, the latter only being dependent on a protocol. It is noticeable that RFC 1630 does not attempt to define at all the notion of resource, actually it barely uses the term besides its occurrence in URI, URL and URN, and still speaks about "Objects of the Network".
RFC 1738 (December 1994) further specifies URLs, the term 'Universal' being changed to 'Uniform'. The document is making a more systematic use of 'resource' to refer to objects which are 'available', or 'can be located and accessed' through the Internet. There again, the term 'resource' itself is not explicitly defined.
== Resources in RDF and the Semantic Web ==
First released in 1999, [[Resource Description Framework | RDF]] was first intended to ''describe'' resources, in other words to declare [[metadata]] of resources in a standard way. A RDF description of a resource is a set of triples (''subject'', ''predicate'', ''object''), where ''subject'' represents the resource to be described, ''predicate'' a type of property relevant to this resource, whereas ''object'' can be data or another resource. The ''predicate'' itself is considered as a resource and identified by a URI. Hence, properties like "title", "author" are represented in RDF as resources, which can be used, in a recursive way, as ''subject'' of other triples.
Building on this recursive principle, RDF vocabularies, such as [[RDFS]], [[Web Ontology Language | OWL]], and [[SKOS]] will pile up definitions of abstract resources such as classes, properties, concepts, all identified by URIs.
=== Using HTTP URIs to identify abstract resources ===
Using URLs, and singularly HTTP URIs, to identify abstract resources, such as classes, properties or other kind of concepts, is a frequent practice, for example in RDFS or OWL [[Ontology (computer science) | ontologies]]. Since such URIs are associated with the HTTP protocol, the question arised of which kind of representation, if any, should be get for such resources through this protocol, typically using a Web browser, and if the syntax of the URI itself could help to differentiate "abstract" resources from "information" resources. The URI specifications such as RFC 3986 let to the protocol specification the task of defining actions performed on the resources and they don't provide any answer to this question. It had been suggested that http URIs identifying a resource in the original sense, file, document or any kind of so-called information resource, should be "slash" URIs, in other words should not contain [[fragment identifier | fragment identifiers]], whereas URIs used to identify concepts or abstract resources should be "hash" URIs using fragment identifiers. For example <nowiki>''http://www.sillywidgets.org/catalogue/widgets.html''</nowiki> would both identify and locate a web page (maybe providing some human-readable description of the widgets selled by Silly Widgets, Inc.) whereas <nowiki>''http://www.widgets.org/ontology#Widget''</nowiki> would identify the abstract concept or class "Widget" in this company ontology, and would not necessarily retrieve any physical resource through http protocol. But it has been answered that such a distinction is impossible to enforce in practice, and famous standard vocabularies provide counter-examples widely used. For example the [[Dublin Core]] concepts such as "title", "publisher", "creator" are identified by "slash" URIs like ''http://purl.org/dc/elements/1.1/title''.
The general question of which kind of resources http URI should or should not identify has been formally known in W3C as the [http://www.w3.org/2001/tag/issues.html#httpRange-14 httpRange-14] issue, following its name on the list defined by the [[Technical Architecture Group]] (TAG). The TAG has delivered in 2005 a final answer to this issue, making the distinction between an "information resource" and a "non-information" resource dependent on the type of answer given by the server to a "GET" request. This solution puts and end to the "hash" vs "slash" debate, and seems to have met a consensus in the Semantic Web community, although some of its prominent members such as [[Patrick Hayes]] have expressed concerns both on its technical feasabilityfeasibility and conceptual foundation. According to Patrick Hayes' view point, the very distinction between "information resource" and "other resource" is impossible to found, and should better not be specified at all, and [[ambiguity]] of the [[referent]] resource is inherent to URIs like to any naming mechanism.
=== Resource ownership, intellectual property and trust ===
[[Category:World Wide Web]]
[[Category:Semantic web ]]
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