Semantic Web Stack
Encyclopedia
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...
.
Overview
The Semantic Web Stack is an illustration of the hierarchy of languages, where each layer exploits and uses capabilities of the layers below. It shows how technologies that are standardized for Semantic WebSemantic 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...
are organized to make the Semantic Web possible. It also shows how Semantic Web is an extension (not replacement) of classical hypertext web.
The illustration was created by Tim Berners-Lee
Tim Berners-Lee
Sir Timothy John "Tim" Berners-Lee, , also known as "TimBL", is a British computer scientist, MIT professor and the inventor of the World Wide Web...
. The stack is still evolving as the layers are concretized .
Semantic Web Technologies
As shown in the Semantic Web Stack, the following languages or technologies are used to create Semantic WebSemantic 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...
. The technologies from the bottom of the stack up to 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...
are currently standardized and accepted to build Semantic Web applications. It is still not clear how the top of the stack is going to be implemented. All layers of the stack need to be implemented to achieve full visions of 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...
.
Hypertext Web technologies
The bottom layers contain technologies that are well known from hypertext web and that without change provide basis for the semantic web.- Internationalized Resource IdentifierInternationalized Resource IdentifierOn 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...
(IRIIRIIRI may refer to:* International Reference Ionosphere a common scientific project of URSI and COSPAR* International Roughness Index, a dimensionless quantity used for measuring road roughness, proposed as a world standard by the World Bank...
), generalization of URIÚriÚriis a village and commune in the comitatus of Pest in Hungary....
, provides means for uniquely identifying semantic web resources. Semantic Web needs unique identification to allow provable manipulation with resources in the top layers. - UnicodeUnicodeUnicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
serves to represent and manipulate text in many languages. Semantic Web should also help to bridge documents in different human languages, so it should be able to represent them. - XMLXMLExtensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
is a markup language that enables creation of documents composed of structured data. Semantic web gives meaning (semantics) to structured data. - XML Namespaces provides a way to use markups from more sources. Semantic Web is about connecting data together, and so it is needed to refer more sources in one document.
Standardized Semantic Web technologies
Middle layers contain technologies standardized by W3C to enable building semantic web applications.- Resource Description FrameworkResource Description FrameworkThe Resource Description Framework is a family of World Wide Web Consortium specifications originally designed as a metadata data model...
(RDF) is a framework for creating statements in a form of so-called triples. It enables to represent information about resources in the form of graph - the semantic web is sometimes called Giant Global GraphGiant Global GraphGiant Global Graph is a name coined by the inventor of the World Wide Web, Tim Berners-Lee in 2007, to help distinguish between the nature and significance of the content on the existing World Wide Web, and that of the next-generation web, or "Web 3.0"...
. - RDF SchemaRDF SchemaRDF Schema is a set of classes with certain properties using the RDF extensible knowledge representation language, providing basic elements for the description of ontologies, otherwise called RDF vocabularies, intended to structure RDF resources...
(RDFS) provides basic vocabulary for RDF. Using RDFS it is for example possible to create hierarchies of classes and properties. - Web Ontology LanguageWeb Ontology LanguageThe 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...
(OWL) extends RDFS by adding more advanced constructs to describe semantics of RDF statements. It allows stating additional constraints, such as for example cardinality, restrictions of values, or characteristics of properties such as transitivity. It is based on description logicDescription logicDescription logic is a family of formal knowledge representation languages. It is more expressive than propositional logic but has more efficient decision problems than first-order predicate logic....
and so brings reasoning power to the semantic web. - SPARQLSPARQLSPARQL is an RDF query language; its name is an acronym that stands for SPARQL Protocol and RDF Query Language. It was made a standard by the RDF Data Access Working Group of the World Wide Web Consortium, and considered as one of the key technologies of semantic web...
is a RDF query language - it can be used to query any RDF-based data (i.e., including statements involving RDFS and OWL). Querying language is necessary to retrieve information for semantic web applications.
Unrealized Semantic Web technologies
Top layers contain technologies that are not yet standardized or contain just ideas that should be implemented in order to realize Semantic Web.- RIFRule Interchange FormatThe Rule Interchange Format is a W3C Recommendation. RIF is part of the infrastructure for the semantic web, along with SPARQL, RDF and OWL...
or SWRLSWRLSWRL is a proposal for a Semantic Web rules-language, combining sublanguages of the OWL Web Ontology Language with those of the Rule Markup Language ....
will bring support of rules. This is important for example to allow describing relations that cannot be directly described using description logic used in OWL. - CryptographyCryptographyCryptography is the practice and study of techniques for secure communication in the presence of third parties...
is important to ensure and verify that semantic web statements are coming from trusted source. This can be achieved by appropriate digital signatureDigital signatureA digital signature or digital signature scheme is a mathematical scheme for demonstrating the authenticity of a digital message or document. A valid digital signature gives a recipient reason to believe that the message was created by a known sender, and that it was not altered in transit...
of RDF statements. - Trust to derived statements will be supported by (a) verifying that the premises come from trusted source and by (b) relying on formal logic during deriving new information.
- User interfaceUser interfaceThe user interface, in the industrial design field of human–machine interaction, is the space where interaction between humans and machines occurs. The goal of interaction between a human and a machine at the user interface is effective operation and control of the machine, and feedback from the...
is the final layer that will enable humans to use semantic web applications.