Resource (Web)
Encyclopedia
The concept of resource is primitive in the 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
s (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).
s or file
s, to a more generic and abstract definition, now encompassing every thing or entity
that can be identified, named, addressed or handled, in any way whatsoever, in the Web at large, or in any networked information system. The declarative aspects of a resource (identification and naming) and its functional aspects (addressing and technical handling) were not clearly distinct in the early specifications of the Web, and the very definition of the concept has been the subject of long and still open debate involving difficult, and often arcane, technical, social, linguistic and philosophical issues.
s (URLs). 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 notable 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.
A resource can be anything that has identity. Familiar examples include an electronic document, an image, a service (e.g., "today's weather report for Los Angeles"), and a collection of other resources. Not all resources are network "retrievable"; e.g., human beings, corporations, and bound books in a library can also be considered resources.
If examples in this document are still limited to physical entities, the definition opens the door to more abstract resources. Providing a concept is given an identity, and this identity is expressed by a well-formed URI (Uniform Resource Identifier, a superset of URLs), then a concept can be a resource as well.
In January 2005, RFC 3986 makes this extension of the definition completely explicit:
…abstract concepts can be resources, such as the operators and operands of a mathematical equation, the types of a relationship (e.g., "parent" or "employee"), or numeric values (e.g., zero, one, and infinity).
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, OWL
, and SKOS
will pile up definitions of abstract resources such as classes, properties, concepts, all identified by URIs.
RDF also specifies the definition of anonymous resources or blank node
s, which are not absolutely identified by URIs.
s , are frequently used to identify abstract resources, such as classes, properties or other kind of concepts. Examples can be found in RDFS or OWL ontologies
. Since such URIs are associated with the HTTP protocol, the question arose of which kind of representation, if any, should one 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 left 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 an HTTP URI identifying a resource in the original sense, such as a file, document, or any kind of so-called information resource, should be "slash" URIs — in other words, should not contain a fragment identifier
, whereas a URI used to identify a concept or abstract resource should be a "hash" URI using a fragment identifier.
For example:http://www.sillywidgets.org/catalogue/widgets.html would both identify and locate a web page (maybe providing some human-readable description of the widgets sold by Silly Widgets, Inc.) whereas http://www.widgets.org/ontology#Widget 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 formerly known in W3C as the 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 an 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 Pat Hayes
have expressed concerns both on its technical feasibility and conceptual foundation. According to Patrick Hayes' view point, the very distinction between "information resource" and "other resource" is impossible to find, and should better not be specified at all, and ambiguity
of the referent resource is inherent to URIs like to any naming mechanism.
World Wide Web
The World Wide Web is a system of interlinked hypertext documents accessed via the Internet...
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 Locator
In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....
s (URLs), but its definition has been further extended to include the referent of any Uniform Resource Identifier
Uniform Resource Identifier
In computing, a uniform resource identifier is a string of characters used to identify a name or a resource on the Internet. Such identification enables interaction with representations of the resource over a network using specific protocols...
(RFC 3986), or Internationalized Resource Identifier
Internationalized Resource Identifier
On the Internet, the Internationalized Resource Identifier is a generalization of the Uniform Resource Identifier . While URIs are limited to a subset of the ASCII character set, IRIs may contain characters from the Universal Character Set , including Chinese or Japanese kanji, Korean, Cyrillic...
(RFC 3987). In the Semantic Web
Semantic Web
The Semantic Web is a collaborative movement led by the World Wide Web Consortium that promotes common formats for data on the World Wide Web. By encouraging the inclusion of semantic content in web pages, the Semantic Web aims at converting the current web of unstructured documents into a "web of...
, abstract resources and their semantic properties are described using the family of languages based on Resource Description Framework
Resource Description Framework
The Resource Description Framework is a family of World Wide Web Consortium specifications originally designed as a metadata data model...
(RDF).
History
The concept of resource has evolved during the Web history, from the early notion of static addressable documentDocument
The term document has multiple meanings in ordinary language and in scholarship. WordNet 3.1. lists four meanings :* document, written document, papers...
s or file
Computer file
A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...
s, to a more generic and abstract definition, now encompassing every thing or entity
Entity
An entity is something that has a distinct, separate existence, although it need not be a material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is animate.An entity could be viewed as a set...
that can be identified, named, addressed or handled, in any way whatsoever, in the Web at large, or in any networked information system. The declarative aspects of a resource (identification and naming) and its functional aspects (addressing and technical handling) were not clearly distinct in the early specifications of the Web, and the very definition of the concept has been the subject of long and still open debate involving difficult, and often arcane, technical, social, linguistic and philosophical issues.
From documents and files to Web resources
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 using Uniform Resource LocatorUniform Resource Locator
In computing, a uniform resource locator or universal resource locator is a specific character string that constitutes a reference to an Internet resource....
s (URLs). 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 notable 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.
From Web resources to abstract resources
The first explicit definition of resource is found in RFC 2396, in August 1998 :A resource can be anything that has identity. Familiar examples include an electronic document, an image, a service (e.g., "today's weather report for Los Angeles"), and a collection of other resources. Not all resources are network "retrievable"; e.g., human beings, corporations, and bound books in a library can also be considered resources.
If examples in this document are still limited to physical entities, the definition opens the door to more abstract resources. Providing a concept is given an identity, and this identity is expressed by a well-formed URI (Uniform Resource Identifier, a superset of URLs), then a concept can be a resource as well.
In January 2005, RFC 3986 makes this extension of the definition completely explicit:
…abstract concepts can be resources, such as the operators and operands of a mathematical equation, the types of a relationship (e.g., "parent" or "employee"), or numeric values (e.g., zero, one, and infinity).
Resources in RDF and the Semantic Web
First released in 1999, RDF was first intended to describe resources, in other words to declare metadataMetadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
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, OWL
Web Ontology Language
The Web Ontology Language is a family of knowledge representation languages for authoring ontologies.The languages are characterised by formal semantics and RDF/XML-based serializations for the Semantic Web...
, and SKOS
SKOS
Simple Knowledge Organization System is a family of formal languages designed for representation of thesauri, classification schemes, taxonomies, subject-heading systems, or any other type of structured controlled vocabulary. SKOS is built upon RDF and RDFS, and its main objective is to enable...
will pile up definitions of abstract resources such as classes, properties, concepts, all identified by URIs.
RDF also specifies the definition of anonymous resources or blank node
Blank node
In RDF, a blank node is a node in an RDF graph representing a resource for which a URI or literal is not given. The resource represented by a blank node is also called an anonymous resource...
s, which are not absolutely identified by URIs.
Using HTTP URIs to identify abstract resources
URLs, particularly HTTP URIUniform Resource Identifier
In computing, a uniform resource identifier is a string of characters used to identify a name or a resource on the Internet. Such identification enables interaction with representations of the resource over a network using specific protocols...
s , are frequently used to identify abstract resources, such as classes, properties or other kind of concepts. Examples can be found in RDFS or OWL ontologies
Ontology (computer science)
In computer science and information science, an ontology formally represents knowledge as a set of concepts within a domain, and the relationships between those concepts. It can be used to reason about the entities within that domain and may be used to describe the domain.In theory, an ontology is...
. Since such URIs are associated with the HTTP protocol, the question arose of which kind of representation, if any, should one 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 left 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 an HTTP URI identifying a resource in the original sense, such as a file, document, or any kind of so-called information resource, should be "slash" URIs — in other words, should not contain a fragment identifier
Fragment identifier
In computer hypertext, a fragment identifier is a short string of characters that refers to a resource that is subordinate to another, primary resource...
, whereas a URI used to identify a concept or abstract resource should be a "hash" URI using a fragment identifier.
For example:
Dublin Core
The Dublin Core metadata terms are a set of vocabulary terms which can be used to describe resources for the purposes of discovery. The terms can be used to describe a full range of web resources: video, images, web pages etc and physical resources such as books and objects like artworks...
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 formerly known in W3C as the 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 an 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 Pat Hayes
Patrick J. Hayes
Patrick John Hayes or Pat Hayes is a British computer scientist who lives and works in the United States. , he is a Senior Research Scientist at the Institute for Human and Machine Cognition in Pensacola, Florida. He received a B.A. in Mathematics from University of Cambridge and a Ph.D...
have expressed concerns both on its technical feasibility and conceptual foundation. According to Patrick Hayes' view point, the very distinction between "information resource" and "other resource" is impossible to find, and should better not be specified at all, and ambiguity
Ambiguity
Ambiguity of words or phrases is the ability to express more than one interpretation. It is distinct from vagueness, which is a statement about the lack of precision contained or available in the information.Context may play a role in resolving ambiguity...
of the referent resource is inherent to URIs like to any naming mechanism.