Semantic Web

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The Semantic Web is a project that intends to create a universal medium for information exchange by giving computer-understandable meaning (semantics) to the content of documents on the World Wide Web. Currently under the direction of the Web's creator, Tim Berners-Lee of the World Wide Web Consortium, the Semantic Web extends the Web through the use of standards, markup languages and related processing tools.

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Potential benefits of the Semantic Web

Humans are capable of using the Web to, say, find the Swedish word for "car", renew a library book, or find the cheapest DVD and buy it. But if you asked a computer to do the same thing, it wouldn't know where to start. That is because web pages are designed to be read by people, not machines. The Semantic Web is a project aimed to make web pages understandable by computers, so that they can search websites and perform actions in a standardized way.

The potential benefits are that computers can harness the enormous network of information and services on the Web. Your computer could, for example, automatically find the nearest manicurist to where you live and book an appointment for you that fits in with your schedule.

A lot of the things that could be done with the Semantic Web could also be done without it, and indeed already are done in some cases. But the Semantic Web provides a standard which makes such services far easier to implement.

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Relationship to the World Wide Web

Currently, the World Wide Web is based primarily on documents written in HyperText Markup Language (HTML), a language that is useful for describing, with an emphasis on visual presentation, a body of structured text interspersed with multimedia objects such as images and interactive forms. HTML has limited ability to classify the blocks of text on a page, apart from the roles they play in a typical document's organization and in the desired visual layout.

For example, with HTML and a tool to render it (perhaps Web browser software, perhaps another user agent), one can create and present a page that lists items for sale. The HTML of this catalog page can make simple, document-level assertions such as "this document's title is 'Widget Superstore'". But there is no capability within the HTML itself to unambiguously assert that, say, item number X586172 is an Acme Gizmo with a retail price of €199, or that it is a consumer product. Rather, HTML can only say that the span of text "X586172" is something that should be positioned near "Acme Gizmo" and "€199", etc. There is no way to say "this is a catalog" or even to establish that "Acme Gizmo" is a kind of title or that "€199" is a price. There is also no way to express that these pieces of information are bound together in describing a discrete item, distinct from other items perhaps listed on the page.

The Semantic Web addresses this shortcoming, using the descriptive technologies Resource Description Framework (RDF) and Web Ontology Language (OWL), and the data-centric, customizable Extensible Markup Language (XML). These technologies are combined in order to provide descriptions that supplement or replace the content of Web documents. Thus, content may manifest as descriptive data stored in Web-accessible databases, or as markup within documents (particularly, in Extensible HTML (XHTML) interspersed with XML, or, more often, purely in XML, with layout/rendering cues stored separately). The machine-readable descriptions enable content managers to add meaning to the content, thereby facilitating automated information gathering and research by computers.

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Components of the Semantic Web

The Semantic Web is comprised of the standards and tools of XML, XML Schema, RDF, RDF Schema and OWL. The OWL Web Ontology Language Overview describes the function and relationship of each of these components of the Semantic Web:

Image:W3c semantic web stack.jpg

  • XML provides a surface syntax for structured documents, but imposes no semantic constraints on the meaning of these documents.
  • XML Schema is a language for restricting the structure of XML documents.
  • RDF is a simple data model for referring to objects ("resources") and how they are related. An RDF-based model can be represented in XML syntax.
  • RDF Schema is a vocabulary for describing properties and classes of RDF resources, with a semantics for generalization-hierarchies of such properties and classes.
  • OWL adds more vocabulary for describing properties and classes: among others, relations between classes (e.g. disjointness), cardinality (e.g. "exactly one"), equality, richer typing of properties, characteristics of properties (e.g. symmetry), and enumerated classes.

The intent is to enhance the usability and usefulness of the Web and its interconnected resources through:

  • documents "marked up" with semantic information (an extension of the HTML <meta> tags used in today's Web pages to supply information for Web search engines using web crawlers). This could be machine-readable information about the human-readable content of the document (such as the creator, title, description, etc., of the document) or it could be purely metadata representing a set of facts (such as resources and services elsewhere in the site). (Note that anything that can be identified with a Uniform Resource Identifier (URI) can be described, so the semantic web can reason about people, places, ideas, cats, etc.)
  • common metadata vocabularies (ontologies) and maps between vocabularies that allow document creators to know how to mark up their documents so that agents can use the information in the supplied metadata (so that Author in the sense of 'the Author of the page' won't be confused with Author in the sense of a book that is the subject of a book review).
  • automated agents to perform tasks for users of the Semantic Web using this metadata
  • web-based services (often with agents of their own) to supply information specifically to agents (for example, a Trust service that an agent could ask if some online store has a history of poor service or spamming).

The primary facilitators of this technology are URIs (which identify resources) along with XML and namespaces. These, together with a bit of logic, form RDF, which can be used to say anything about anything. As well as RDF, many other technologies such as Topic Maps and pre-web artificial intelligence technologies are likely to contribute to the Semantic Web.

A popular application of the Semantic Web is Friend of a Friend (or FoaF), which describes relationships among people and other agents in terms of RDF.

An implementation of a Semantic Web Browser is the BigBlogZoo. Over 60,000 xml feeds have been categorised using the DMOZ schema and can be spidered. It is free. The commercial version, MediaMiner, allows you to mine these feeds for information.

Another freely downloadable tool is the new plug-in to Firefox, Piggy Bank. Piggy Bank works by extracting or translating web scripts into RDF information and storing this information on the user’s computer. This information can then be retrieved independently of the original context and used in other contexts, for example by using Google Maps to display information. Piggy Bank works with a new service, Semantic Bank, which combines the idea of tagging information with the new web languages. Piggy Bank was developed by the Simile Project, which also provides RDFizers, tools that can be used to translate specific types of information, for example weather reports for US zip codes, into RDF. Efforts like these could ease a potentially troublesome transition between the web of today and its semantic sucessor.

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See also

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References

  • {{cite book 
|    author = Michael C. Daconta, Leo J. Obrst, Kevin T. Smith
|      date = 2003-05-30
|     title = The Semantic Web: A Guide to the Future of XML, Web Services, and Knowledge Management
| publisher = John Wiley & Sons
|        id = ISBN 0-471-43257-1
}}
  • {{cite book 
|    author = Dieter Fensel, Wolfgang Wahlster, Henry Lieberman, James Hendler
|      date = 2002-11-15
|     title = Spinning the Semantic Web: Bringing the World Wide Web to Its Full Potential
| publisher = MIT Press
|        id = ISBN 0-262-06232-1
}}
  • {{cite book 
|    author = Steffen Staab, Rudi Studer
|      year = 2004
|     month = January
|     title = Handbook on Ontologies
| publisher = Heidelberg: Springer Verlag
|        id = ISBN 3-540-40834-7
}}
  • {{cite book 
|      date = 2003-01-17
|     title = Visualizing the Semantic Web
|    editor = Vladimir Geroimenko, Chaomei Chen (Eds.)
| publisher = Springer Verlag
|        id = ISBN 1-85233-576-9
}}
  • {{cite book 
|    author = John Davies, Dieter Fensel, Frank van Harmelen
|      date = 2003-01-21
|     title = Towards the Semantic Web: Ontology-Driven Knowledge Management
| publisher = John Wiley & Sons
|        id = ISBN 0-470-84867-7
}}
  • {{cite book 
|    author = Grigoris Antoniou, Frank van Harmelen
|      date = 2004-04-01
|     title = A Semantic Web Primer
| publisher = The MIT Press
|        id = ISBN 0-262-01210-3
}}
  • {{cite book 
|    author = Jeffrey T. Pollock, Ralph Hodgson
|      date = 2004-07-21
|     title = Adaptive Information: Improving Business through Semantic Interoperability, Grid Computing, and Enterprise Integration
| publisher = John Wiley
|        id = ISBN 0-471-48854-2
}}
  • {{cite book 
|    author = Bo Leuf
|      date = 2006
|     title = The Semantic Web: Crafting Infrastructure for Agency
| publisher = John Wiley
|        id = ISBN 0-470-01522-5
}}
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External links

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Articles

Tools

  • Altova SemanticWorks Visual RDF and OWL editor that auto-generates RDF/XML or nTriples based on visual ontology design
  • Protégé Opensource visual ontology editor written in Java. Protégé has an architecture that allows users to develop plug-in tools. Existing plug-ins allow the use of various formats including OWL and RDF, and visualisation of ontologies in different ways.
  • Jena Opensource ontology API written in Java. Jena supports the programic loading, reading, and editing of OWL and DAML ontologies. Protégé uses Jena for its OWL implementation.
  • Swoogle A search engine for online semantic web ontologies, documents, and terms(URIs).
  • LuMriX A commercial search engine using Semantic Web Technologies (XML and XML Topic Maps).
  • Semantical An open source search engine based on Semantic Web standards.
  • Model Futures OWL Editor (Beta) - a simple tool for working with OWL
  • ekoss.org - A collaborative knowledge sharing environment where model developers can submit advertisements of the models that they have developed.ca:Web semàntica

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