Introduction to concepts of the semantic web

1. The Semantic Web
A new form of Web Content that is meaningful to Computers
By
Tim Berners-Lee, James Hendler and Oral Lassila
[Scientific American: Feature Article – May 2001]
Presented By: Prasad Fernando / 3023924
Friday 27th February 2015

2. The Semantic Web (web 3.0) is an idea of World Wide Web inventor Tim
Berners-Lee that the Web as a whole can be made more intelligent and
perhaps even intuitive about how to serve a user's needs.

3. Motivation behind Semantic Web
• Not 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.

4. Why HTML is not good ?
• Currently, the World Wide Web is based mainly on documents
written in HTML; 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 Representation

5. Knowledge Representation
XML: Extensible Markup Language
RDF: Resource Description Framework
OWL: Ontology Web Language
HTML describes documents and the links between them. RDF, OWL, and XML, by
contrast, can describe arbitrary things such as people, meetings, or airplane parts.

6. Knowledge Representation
• WWW is document sharing - But the semantic web is data
sharing. 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 ?

7. XML – Extensible Markup Language
• XML 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.

8. 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: <item rdf:about=“http://bppfernando.blogspot.com/”>Prasad</item>
• URIs ensure that concepts are not just words in a document but
are tied to a unique definition that everyone can find on the web.

9. 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 issue
• The 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.

10. The Semantic Web Stack

11. Semantic Web for Software Agents
• Machine readable web contents and automated services (other
agents) for the agents that collect, process and transform
information from diverse sources
• Exchange 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.

12. Agents – Cont’d.
• 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

13. Evaluation of Knowledge
• If properly designed, the semantic web can assist the evaluation of human
knowledge as a whole
• Since 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.

14. Challenges
for the Semantic Web
• Vastness – 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 values
• Inconsistency – Logical contradiction encountered when
combining ontologies form different sources.
• Deception – Producer of the information is intentionally
misleading the consumer of the information.