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The Semantic Web
The Semantic WebA new form of Web Content that is meaningful to ComputersByTim Berners-Lee, James Hendler and Oral Lassila[Scientific American: Feature Article May 2001]Presented By: Prasad Fernando / 3023924Friday 27th February 2015
The Semantic Web (web 3.0) is an idea of World Wide Web inventorTim Berners-Leethat the Web as a whole can be made more intelligent and perhaps even intuitive about how to serve a user's needs.Motivation behind Semantic WebNot a separate web, but an extension of the current one, in which information is given well defined meaning; enabling computers and people to work in corporation.Will bring structure to the meaningful content of Web Pages, creating an environment for software agents roaming from page to page can carry out sophisticated tasks four users.With the access to structured collection of information and sets of inference rules, Computers can conduct automated reasoning on the Semantic Web.Add logic to the Web The means to use rules to make inference, to choose courses of action and to answer questions.
Why HTML is not good ?Currently, the World Wide Web is based mainly on documents written inHTML; that is used for coding a body of text along with multimedia objects.No capability within the HTML itself to assert unambiguously Ex: the item number X586172 is an Camera with a retail price of $199. Rather, HTML can only say that the span of text "X586172" is something that should be positioned near Camera" and $199. There is also no way to express that these pieces of information are bound together in describing a discrete item, distinct from other items listed on the page.Knowledge RepresentationKnowledge Representation
XMLRDFOWLSemantic WebXML: Extensible Markup LanguageRDF: Resource Description FrameworkOWL: Ontology Web LanguageHTML describes documents and the links between them. RDF, OWL, and XML, by contrast, can describe arbitrary things such as people, meetings, or airplane parts.
Knowledge RepresentationWWW is document sharing - But the semantic web is data sharing. So the resulting network of linked data is a global graphHow the Giant Global Graph is builtA URL should point to the dataAnyone accessing the URL should get data backRelationships in the data should point to additional URLs with dataWhat is new ?XML Extensible Markup LanguageXML Lets everyone create their own tags that annotate Web Pages or sections of text on a page. Even though XML allows users to add arbitrary structure to their documents, it says nothing about what the structures mean.
RDF Resource Description Framework The meaning of the structures that XML cannot express can be expressed by RDF.RDF encodes structures in sets of triples where each triple being rather like a subject, verb, object of an elementary sentence.Subject, Verb, Object are identified by Uniform Resource Locator (URI) - just like a link in a web page.Ex: PrasadURIs ensure that concepts are not just words in a document but are tied to a unique definition that everyone can find on the web.Ontology Theory about nature of exist A program that wants to compare or combine information across the two databases has to know that these two terms are being used to mean the same thing Collection of information called ontology will solved this issueThe most typical type kind of ontology for the web has a taxonomy and a set of inference rules.Now, the meaning of the XML codes used on web pages can be defined by pointers from the page to an ontology.Ontology helps the search engines to look for relevant pages.Can be used to tackle complicated question based on many pages.
The Semantic Web Stack
Semantic Web for Software AgentsMachine readable web contents and automated services (other agents) for the agents that collect, process and transform information from diverse sourcesExchange of proof written in the Semantic Web Unifying Language The language which express logical inference made using rules and information.Usage of Digital Signatures Agents should be skeptical of assertion that they read on the semantic web until they have checked the source of information.Service Discovery The consumer and producer agents can reach a shared understanding by exchanging ontologies.
Agents Contd.Creation of Value Chain subassemblies of information are passed from agent to agent, each one adding value to construct the final product requested by the end user.Automation of physical devices URI can point to anything including physical devices. RDF can be used to describe devices such that devices can advertise their functionality like software agents.Ex: Web enabled microwave oven consulting the frozen-food manufacturer website for optimal cooking parameters
Evaluation of KnowledgeIf properly designed, the semantic web can assist the evaluation of human knowledge as a wholeSince semantic web name every concept by a URI, anyone can express new concepts that they invented with minimal effort. The unifying logical language will enable these concepts to be progressively linked into universal web.
Challenges for the Semantic WebVastness Current WWW contains millions of pages so that automated reasoning system have to deal with ontology with a lot of classes.Vagueness The relative concepts such as tall and thin make it difficult to match queries.Uncertainty Reasoning with probability valuesInconsistency Logical contradiction encountered when combining ontologies form different sources.Deception Producer of the information is intentionally misleading the consumer of the information.