The Semantic Web

A new form of Web Content that is meaningful to ComputersBy

Tim 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 inventor TimBerners-Lee that the Web as a whole can be made more intelligent andperhaps even intuitive about how to serve a user's needs.

Motivation behind Semantic Web

• Not a separate web, but an extension of the current one, inwhich information is given well defined meaning; enablingcomputers and people to work in corporation.

• Will bring structure to the meaningful content of Web Pages,creating an environment for software agents roaming from pageto page can carry out sophisticated tasks four users.

• With the access to structured collection of information and setsof inference rules, Computers can conduct automatedreasoning on the Semantic Web.

• Add logic to the Web – The means to use rules to makeinference, to choose courses of action and to answer questions.

Why HTML is not good ?

• Currently, the World Wide Web is based mainly on documentswritten in HTML; that is used for coding a body of text alongwith 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 somethingthat should be positioned near “Camera" and “$199”.

• There is also no way to express that these pieces of informationare bound together in describing a discrete item, distinct fromother items listed on the page.

Knowledge Representation

Knowledge Representation

XML: Extensible Markup LanguageRDF: Resource Description Framework

OWL: Ontology Web Language

HTML describes documents and the links between them. RDF, OWL, and XML, bycontrast, can describe arbitrary things such as people, meetings, or airplane parts.

Knowledge Representation

• WWW is document sharing - But the semantic web is datasharing. So the resulting network of linked data is a global graph

• How the Giant Global Graph is built– A URL should point to the data

– Anyone accessing the URL should get data back

– Relationships in the data should point to additional URLs with data

What is new ?

XML – Extensible Markup Language

• XML Lets everyone create their own tags thatannotate Web Pages or sections of text on a page.

• Even though XML allows users to add arbitrarystructure to their documents, it says nothing aboutwhat the structures mean.

RDF – Resource Description Framework

• The meaning of the structures that XML cannot express can beexpressed by RDF.

• RDF encodes structures in sets of triples where each triple beingrather 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: <item rdf:about=“http://bppfernando.blogspot.com/”>Prasad</item>

• URIs ensure that concepts are not just words in a document butare 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 acrossthe two databases has to know that these two terms are beingused to mean the same thing – Collection of information calledontology will solved this issue

• The most typical type kind of ontology for the web has a taxonomyand a set of inference rules.

• Now, the meaning of the XML codes used on web pages can bedefined 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 Agents

• Machine readable web contents and automated services (otheragents) for the agents that collect, process and transforminformation from diverse sources

• Exchange of proof written in the Semantic Web UnifyingLanguage – The language which express logical inference madeusing rules and information.

• Usage of Digital Signatures – Agents should be skeptical ofassertion that they read on the semantic web until they havechecked the source of information.

• Service Discovery – The consumer and producer agents can reacha shared understanding by exchanging ontologies.

Agents – Cont’d.

• Creation of Value Chain – subassemblies of information arepassed from agent to agent, each one adding value to constructthe final product requested by the end user.

• Automation of physical devices – URI can point to anythingincluding physical devices. RDF can be used to describe devicessuch that devices can advertise their functionality like softwareagents.– Ex: Web enabled microwave oven consulting the frozen-food

manufacturer website for optimal cooking parameters

Evaluation of Knowledge

• If properly designed, the semantic web can assist the evaluation of humanknowledge as a whole

• Since semantic web name every concept by a URI, anyone can express newconcepts that they invented with minimal effort. The unifying logical languagewill enable these concepts to be progressively linked into universal web.

Challenges for the Semantic Web

• Vastness – Current WWW contains millions of pages so thatautomated reasoning system have to deal with ontology with alot of classes.

• Vagueness – The relative concepts such as tall and thin make itdifficult to match queries.

• Uncertainty – Reasoning with probability values

• Inconsistency – Logical contradiction encountered whencombining ontologies form different sources.

• Deception – Producer of the information is intentionallymisleading the consumer of the information.