The Semantic Web is a project that intends to create a universal medium for information exchange by putting documents with computer-processable meaning (semantics) 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.
Potential benefits of the Semantic Web
Humans are capable of using the Web, say, to find the Swedish word for "car," to reserve a library book, or to search for 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.
Currently there is much data on our computers which we cannot browse, or process by, for example, pulling into a spreadsheet, graphing it or joining it with other data. This includes personal data like calendars, playlists, GPS tracks, and bank statements; enterprise data product and workflow and resources, and public data such as weather, events and the properties of materials.
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.
Relationship to the Hypertext 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.
The Semantic Web comprises the standards and tools of XML, Resource Description Framework (RDF), and Web Ontology Language (OWL).
- 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 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 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.
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 successor.
- Semantic Web Overview
- OWL Web Ontology Language Overview
- W3C Semantic Web initiative
- Tim Berners-Lee's 1998 roadmap paper
- Semantic Web Community Portal
- The Rule Markup Initiative
- DERI - Digital Enterprise Research Institute
- The Road to the Semantic Web from the Read/Write Web
- Entrepreneurs See a Web Guided by Common Sense from the New York Times (free subscription required)
- The race to create a 'smart' Google from CNN
- ebizQ: Can We Develop a Semantic Name Service? by Chris Harding (2005)
- CodeProject: Music and the semantic web By Chris Mitchell (2006)
- ebizQ: Achieving Semantic Interoperability by Chris Harding (2005)
- Digital Divide Network: Tim Berners-Lee: Weaving the Semantic Web by Andy Carvin (2004)
- FreePint: Libby Miller and Simon Price: The Semantic Web is Your Friend (2004)
- ZDnet: W3C recommends Semantic Web specs (2004)
- Scientific American: The Semantic Web: A new form of Web content that is meaningful to computers will unleash a revolution of new possibilities By Tim Berners-Lee, James Hendler and Ora Lassila (May 2001)
- Semantic Web reading material from ZDNet's Between the Lines blog (3.26.07)
- 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.
- GrOWL Open source graphical ontology browser and editor. GrOWL allows users to browse large ontologies with advanced navigation tools and incorporates a full OWL graphical editor.
- 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.
- swoop - A Hypermedia-based Featherweight OWL Ontology Editor, with Web Browser like look & feel.
- The latest Wikipdia dump in RDF
- UniProt protein sequence and annotation data in RDF
- SWETO - Semantic Web Technology Evaluation Ontology
- International Journal on Semantic Web and Information Systems (IJSWIS)
- Journal of Web Semantics
- Applied Ontology