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The Semantic Web is a "web of data" that enables machines to understand the semantics, or meaning, of information on the World Wide Web. It extends the network of hyperlinked human-readable web pages by inserting machine-readable metadata about pages and how they are related to each other, enabling automated agents to access the Web more intelligently and perform tasks on behalf of users. The term "Semantic Web" is often used more specifically to refer to the formats and technologies that enable it. These technologies include the Resource Description Framework (RDF), a variety of data interchange formats (e.g. RDF/XML, N3, Turtle, N-Triples), and notations such as RDF Schema (RDFS) and the Web Ontology Language (OWL), all of which are intended to provide a formal description of concepts, terms, and relationships within a given knowledge domain.

diagram showing concept of Semantic Web layers

  • GGG (Giant Global Graph) Resource List - X
    Tim Berners-Lee thinks about the social network itself that is inside and between social-network Web sites such as Facebook. He assumes that people can use the word "Graph" to distinguish these from the "Web". Then he says that, although he called this graph the Semantic Web, maybe it should have been called the "Giant Global Graph".


The following concepts are considered parts of the Semantic Web. Below are the components which make up various parts of Semantic Web implementations.

Representation (Decreasing order of complexity)

  • RDF Schema Resource List
    RDF Schema (variously abbreviated as RDFS, RDF(S), RDF-S, or RDF/S) is an extensible knowledge representation language, providing basic elements for the description of ontologies, otherwise called Resource Description Framework (RDF) vocabularies, intended to structure RDF resources.
  • N3 (Notation 3) Resource List
    Notation3, or N3 as it is more commonly known, is a shorthand non-XML serialization of Resource Description Framework models, designed with human-readability in mind: N3 is much more compact and readable than XML RDF notation. N3 has several features that go beyond a serialization for RDF models, such as support for RDF-based rules. Turtle is a simplified, RDF-only subset of N3.
  • Turtle (Terse RDF Triple Language) Resource List
    Turtle (Terse RDF Triple Language) is a serialisation format for RDF (Resource Description Framework) graphs. A subset of Tim Berners-Lee and Dan Connolly's Notation 3 (N3) language, it was defined by Dave Beckett, and is a superset of the minimal N-Triples format. Unlike full N3, Turtle doesn't go beyond RDF's graph model. The SPARQL Protocol and RDF Query Language uses a similar N3 subset to Turtle for its graph patterns, but using N3's braces syntax for delimiting subgraphs.
  • N-Triples Resource List
    N-Triples is a format for storing and transmitting data. It is a line-based, plain text serialisation format for RDF (Resource Description Framework) graphs, and a subset of the Turtle (Terse RDF Triple Language) format. N-Triples should not be confused with Notation 3 which is a superset of Turtle. N-Triples was primarily developed by Dave Beckett at the University of Bristol and Art Barstow at the W3C.
    N-Triples was designed to be a simpler format than Notation 3 and Turtle, and therefore easier for software to parse and generate. However, because it lacks some of the shortcuts provided by other RDF serialisations (such as CURIEs and nested resources, which are provided by both RDF/XML and Turtle) it can be onerous to type out large amounts of data by hand, and difficult to read.


  • RDFa (Resource Description Framework-in-attributes) - X
    RDFa (or Resource Description Framework - in - attributes) is a W3C Recommendation that adds a set of attribute level extensions to XHTML for embedding rich metadata within Web documents. The RDF data model mapping enables its use for embedding RDF triples within XHTML documents, it also enables the extraction of RDF model triples by compliant user agents.
  • SAWSDL (Semantic Annotations for WSDL) Resource List - X
    The Semantic Annotations for WSDL and XML Schema (SAWSDL) W3C Recommendation defines mechanisms using which semantic annotations can be added to WSDL components. SAWSDL does not specify a language for representing the semantic models, e.g. ontologies. Instead, it provides mechanisms by which concepts from the semantic models that are defined either within or outside the WSDL document can be referenced from within WSDL components as annotations. These semantics when expressed in formal languages can help disambiguate the description of Web services during automatic discovery and composition of the Web services.


  • SPARQL (SPARQL Protocol and RDF Query Language) Resource List
    SPARQL (pronounced "sparkle") is an RDF query language; its name is a recursive acronym that stands for SPARQL Protocol and RDF Query Language. It was standardized by the RDF Data Access Working Group (DAWG) of the World Wide Web Consortium, and is considered a key semantic web technology. SPARQL allows for a query to consist of triple patterns, conjunctions, disjunctions, and optional patterns.
  • SPASQL (SPARQL SQL) Resource List - X
    SPASQL is simply an extension of the SQL standard, allowing execution of SPARQL queries within SQL statements, typically by treating them as subquery or function clauses. Implementations of this SQL extension may be internal to the DBMS engine, as in OpenLink Virtuoso (see docs), or delivered through an extension architecture, as in the SPASQL module for MySQL.


  • RIF (Rule Interchange Format) Resource List - X
    The Rule Interchange Format (RIF) is a W3C Recommendation. RIF is part of the infrastructure for the semantic web, along with (principally) RDF and OWL. Although originally envisioned by many as a "rules layer" for the semantic web, in reality the design of RIF is based on the observation that there are many "rules languages" in existence, and what is needed is to exchange rules between them.
    RIF includes three dialects, a Core dialect which is extended into a Basic Logic Dialect (BLD) and Production Rule Dialect (PRD).
  • SWRL (Semantic Web Rule Language) Resource List - X
    SWRL (Semantic Web Rule Language) is a proposal for a Semantic Web rules-language, combining sublanguages of the OWL Web Ontology Language (OWL DL and Lite) with those of the Rule Markup Language (Unary/Binary Datalog). SWRL has the full power of OWL DL, but at the price of decidability and practical implementations. Rules are of the form of an implication between an antecedent (body) and consequent (head). The intended meaning can be read as: whenever the conditions specified in the antecedent hold, then the conditions specified in the consequent must also hold.


  • Linked Data Resource List - X
    Linked Data describes a method of publishing structured data, so that it can be interlinked and become more useful. It builds upon standard Web technologies, such as HTTP and URIs - but rather than using them to serve web pages for human readers, it extends them to share information in a way that can be read automatically by computers. This enables data from different sources to be connected and queried.


  • FOAF (Friend of a Friend) Resource List
    FOAF (an acronym of Friend of a friend) is a machine-readable ontology describing persons, their activities and their relations to other people and objects. Anyone can use FOAF to describe him or herself. FOAF allows groups of people to describe social networks without the need for a centralised database. FOAF is a descriptive vocabulary expressed using the Resource Description Framework (RDF) and the Web Ontology Language (OWL).
  • Dublin Core Resource List
    The Dublin Core set of metadata elements provides a small and fundamental group of text elements through which most resources can be described and catalogued. Using only 15 base text fields, a Dublin Core metadata record can describe physical resources such as books, digital materials such as video, sound, image, or text files, and composite media like web pages. Metadata records based on Dublin Core are intended to be used for cross-domain information resource description and have become standard in the fields of library science and computer science. Implementations of Dublin Core typically make use of XML and are Resource Description Framework based.


  • 4store
    4store is a database storage and query engine that holds RDF data. It has been used by Garlik as their primary RDF platform for three years, and has proved itself to be robust and secure. 4store's main strengths are its performance, scalability and stability. It does not provide many features over and above RDF storage and SPARQL queries, but if your are looking for a scalable, secure, fast and efficient RDF store, then 4store should be on your shortlist.
  • D2R
    D2R Server is a tool for publishing relational databases on the Semantic Web. It enables RDF and HTML browsers to navigate the content of the database, and allows applications to query the database using the SPARQL query language.
  • Jena
    Jena is an open source Semantic Web framework for Java. It provides an API to extract data from and write to RDF graphs. The graphs are represented as an abstract "model". A model can be sourced with data from files, databases, URLs or a combination of these. A Model can also be queried through SPARQL and updated through SPARUL.
  • Sesame
    Sesame is an open-source framework for querying and analyzing RDF data. It was created, and is still being maintained, by the Dutch software company Aduna. It was originally developed as part of the "On-To-Knowledge", a semantic web project that ran from 1999 to 2002. It contains a triplestore.
  • Spyder
    Spyder creates a SPARQL 1.1 endpoint for any relational database, providing the ability to merge data from any relational store, regardless of its location.
  • Ultrawrap
    Ultrawrap is an automatic Relational Database to RDF (RDB2RDF) system that implements a SPARQL query interface on legacy relational databases.

RDF/SPARQL access to relational databases

  • DartQuery is a component of the DartGrid application framework which rewrites SPARQL queries as SQL against legacy relational databases.
  • SPASQL is an open-source module compiled into the MySQL server to give MySQL native support for RDF.
  • SquirrelRDF supports access to LDAP directories in addition to relational databases.
  • Triplify is a small plugin for Web applications, which reveals the semantic structures encoded in relational databases by making database content available as RDF, JSON or Linked Data.
  • Virtuoso seems to have use pretty smart rewriting algorithm and also supports Named Graphs.


  • bioCatalogue
    A curated catalog of Life Science Web Services
  • DBPedia Resource List
    DBpedia is a project aiming to extract structured content from the information created as part of the Wikipedia project. This structured information is then made available on the World Wide Web. DBpedia allows users to query relationships and properties associated with Wikipedia resources, including links to other related datasets. [
  • Granatum
    A social collaborative working space semantically interlinking biomedical researchers, knowledge and data for the design and execution of in-silico models and experiments in cancer chemoprevention.
  • Gruff
    Gruff is a graphical triplestore browser that attempts to make data retrieval more pleasant and powerful with a variety of tools for laying out cyclical graphs, displaying tables of properties, managing queries, and building SPARQL and queries as visual diagrams.
  • LinkedGeoData
    LinkedGeoData is an effort to add a spatial dimension to the Web of Data / Semantic Web. LinkedGeoData uses the information collected by the OpenStreetMap project and makes it available as an RDF knowledge base according to the Linked Data principles. It interlinks this data with other knowledge bases in the Linking Open Data initiative.
  • Linked Open Data Resource List
    The goal of the W3C SWEO Linking Open Data community project is to extend the Web with a data commons by publishing various open data sets as RDF on the Web and by setting RDF links between data items from different data sources. RDF links enable you to navigate from a data item within one data source to related data items within other sources using a Semantic Web browser. RDF links can also be followed by the crawlers of Semantic Web search engines, which may provide sophisticated search and query capabilities over crawled data. As query results are structured data and not just links to HTML pages, they can be used within other applications.
  • Linked Open Vocabularies Resource List
    The LOV dataset contains the description of RDFS vocabularies or OWL ontologies defined for and used by datasets in the Linked Data Cloud. Whenever available each vocabulary includes references to the datasets using it, in particular those listed in CKAN. The descriptions use in particular the VOAF vocabulary to state different ways such vocabularies can rely on, extend, specify, annotate or otherwise link to each other, and reuse a lot of vocabularies it describes, such as Dublin Core, voiD, BIBO, and many more.
  • Semantic Media Wiki Resource List
    Semantic MediaWiki (SMW) is an extension to MediaWiki, that allows for annotating semantic data within wiki pages, thus turning a wiki that incorporates the extension into a semantic wiki. Data that has been encoded can be used in semantic searches, used for aggregation of pages, displayed in formats like maps, calendars and graphs, and exported to the outside world via formats like RDF and CSV.
  • SMART (Semantic web information Management with Automated Reasoning Tool) Resource List
    SMART (Semantic web information Management with automated Reasoning Tool) is an open-source project, which aims to provide intuitive tools for life scientists for represent, integrate, manage and query heterogeneous and distributed biological knowledge. SMART was designed with interoperability and extensibility in mind and uses AJAX, SVG and JSF technologies, RDF, OWL, SPARQL semantic web languages, triple stores (i.e. Jena) and DL reasoners (i.e. Pellet) for the automated reasoning. Features include semantic query composition and validation using DL reasoners, a graphical representation of the query, a mapping of DL queries to SPARQL, and the retrieval of pre-computed inferences from an RDF triple store.
  • Web 3.0 Resource List
    Definitions of Web 3.0 vary greatly. Some believe its most important features are the Semantic Web and personalization. According to some Internet experts Web 3.0 will allow the user to sit back and let the Internet do all of the work for them. Rather than having search engines gear towards your keywords, the search engines will gear towards the user. Keywords will be searched based on your culture, region, and jargon.

Semantic Web

  • A Semantic Web Primer
    A collection of powerPoint presentations which outline the basics of the Semantic Web.
  • Foundations of Semantic Web Technologies
    By Pascal Hitzler, Markus Krötzsch, Sebastian Rudolph
  • Presents current developments in semantic web standards, covering RDF, RDF schema, OWL 2, RIF, and SPARQL
  • Provides a thorough treatment of formal semantics, including proof theory
  • Explores querying OWL, the relationship between rules and OWL, and ontology engineering and applications.
  • Separates syntax and language from in-depth treatments of the formal foundations."
  • Semantic Web for the Working Ontologist
    By Dean Allemang, Jim Hendler
    Provides practical information for all programmers and subject matter experts engaged in modeling data to fit the requirements of the Semantic Web. De-emphasizes algorithms and proofs, focusing instead on real-world problems, creative solutions, and highly illustrative examples. Presents detailed, ready-to-apply recipes for use in many specific situations. Shows how to create new recipes from RDF, RDFS, and OWL constructs.