Transcript Document

Introduction to
Semantic Web
Teeratorn Saneeyeng
Department of Computer Education
King Mongkut’s University of Technology North Bangkok
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Outline
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Background
Semantic Web
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Definitions
How Will the Semantic Web Work?
Ontologies
RDF (Resource Description Framework)
Semantic Web Examples
Conclusion
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Background
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Human are capable of using the Web to carry out
tasks such as;
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Finding the German word for “Morning”
Searching and reserving books from library
Searching for a low price for a DVD
etc.
However, a computer cannot accomplish the
tasks without human direction because;
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Web pages are designed to be read by human, not
machines
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Background
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A complex user query can be a big problem in finding
information on the Web.
A query for “professor in faculty of engineering in universities
in the United States” may return results from the Web pages
from the other countries other than the United States.
Most documents on the Web not only contain text
 also immense amount of images, sounds, video and other
multimedia files,
 these files are meaningless to computers.
Semantic Web is a vision of information that is
understandable by computers, so that they can perform
more of the tedious works involved in finding, sharing, and
combining information on the Web.
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Background
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Semantic Web will overcome such the
problems by making the Web not only
human-understandable but also machineunderstandable.
Semantic Web is a vision of information
that is understandable by computers, so
that they can perform more of the tedious
works involved in finding, sharing, and
combining information on the Web.
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Background
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Tim Berners-Lee expressed the vision of
the Semantic Web as follows:
I have a dream for the Web [in which computers] become
capable of analyzing all the data on the Web – the content,
links, and transactions between people and computers. A
‘Semantic Web’, which should make this possible, has yet to
emerge, but when it does, the day-to-day mechanisms of
trade, bureaucracy, and our daily lives will be handled by
machines talking to machines. The ‘intelligent agents’ people
have touted for ages will finally materialize.
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Semantic Web
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It derives from W3C1 director Sir Tim Berners-Lee's
vision of the Web as a universal medium for data,
information, and knowledge exchange.
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The word semantics stand for the meaning of. The
semantics of something is the meaning of something.
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The Semantic Web is a web that is able to describe
things in a way that computers can understand.
 The Beatles was a popular band from Liverpool.
 John Lennon was a member of the Beatles.
 The record "Hey Jude" was recorded by the
Beatles.
1. W3C (World Wide Web Consortium) is a forum for information, commerce,
communication, and collective understanding. W3C was founded in Oct. 1994.
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Semantic Web (Cont’d)
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Statements are built with syntax rules
 The syntax of a language defines the rules for
building the language statements. But how can
syntax become semantic?
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This is what the Semantic Web is all about:
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Describing things in a way that computer applications can
understand.
The Semantic Web is not about links between Web pages.
The Semantic Web describes the relationships among
things (e.g., A is a part of B and Y is a member of Z) and
the properties of things (e.g., size, weight, age, and price).
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Semantic Web (Cont’d)
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Semantic Web (SW), proposed by W3C, is one of the
most promising and accepted approaches to make
the Web content becomes more machine-readable so
that intelligent agents can retrieve and process
information readily [Dong and Dan 05].
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The SW is a vision of the next generation of the
WWW in which information is given well-defined
meaning understandable by machines as well as
humans [Lei 05].
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Why is there a need for the Semantic Web?
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Knowledge Management
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With the large number of documents made available
online by organizations, several document management
systems have entered the market. However, these
systems have severe weaknesses [Fensel et al. 03]:
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Searching information: Existing keyword-based search
retrieves irrelevant information that uses keyword in a context
other than the one in which the searcher is interested.
Extracting information: Human browsing and reading is
currently required to extract relevant information from
information sources, as automatic agents lack the common
sense knowledge required to extract such information from
textual representations and fail to integrate information spread
over different sources.
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Why is there a need for the Semantic Web? (Cont’d)
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Maintenance: Maintaining weakly-structured text sources is a
difficult and time-consuming activity when such sources become
large.
Automatic document generation: Adaptive Web sites that
enable a dynamic reconfiguration of information according to
user profiles or other relevant aspects would be very useful.
Semantic Web technology will enable structural and
semantic definitions of documents providing
completely new possibilities:
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Intelligent search instead of keyword matching.
Query answering instead of information retrieval.
Document exchange among departments via ontology
mapping.
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Why is there a need for the Semantic Web? (Cont’d)
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Web Commerce
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Very early on in B2C (Business to Customer)
development, shopbots were developed that visit
several stores, extract product information, and
present to the customer an instant market overview.
Their functionality is provided via wrappers written
for each online store. Such wrappers use a keyword
search together with assumptions on regularities in
the presentation format of stores’ Web sites and text
extraction heuristics, to find information about the
requested product and return it to the customer.
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Why is there a need for the Semantic Web? (Cont’d)
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Web Commerce (Cont’d)
 However, this technology has two severe limitations:
 Effort: Writing a wrapper for each online store is
a time-consuming activity, and changes in the
layout of stores may result in high levels of
required maintenance to keep the wrappers upto-date.
 Quality: The product information extracted by
shopbots using such technology is limited (mostly
price information), error prone, and incomplete.
 For example, a wrapper may extract the direct
price of product but miss indirect costs such as
shipping, or discount.
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How Will the Semantic Web Work?
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In order to organize Web content, AI
researchers proposed a series of conceptual
models.
The central idea is to categorize information
in a standard way.
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Similar to the solution used to classify living
beings
Biologists use a well-defined taxonomy. Likewise,
computer scientists are looking for similar model
to help structure Web content
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Concepts
• Metadata
• Ontologies
• Ontology Languages
• Web Services
Semantic
Web
Applications
Technologies
Themes related to the Semantic Web [Breitman et al. 07]
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How Will the Semantic Web Work?
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Metadata
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Metadata is “data about data”
They serve to index Web pages and Web
sites in the Semantic Web
Allowing other computers to acknowledge
what a Web page is about
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How Will the Semantic Web Work?
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Ontologies
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In computer science, ontologies were
adopted in AI to facilitate knowledge
sharing and reuse [Fensel 01]
Becoming widespread in areas:
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Intelligent information integration
Cooperative information systems
Agent-based software engineering
E-commerce
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How Will the Semantic Web Work?
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Ontologies
Sample ontology of a Computer Science Department [Doan et al. 03]
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How Will the Semantic Web Work?
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Ontology Languages
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Designed to define ontologies
They are sometimes called:
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Lightweight ontology languages
Web-based ontology languages
Markup ontology languages
RDF (Resource Description Language)
OWL (Web Ontology Language)
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How Will the Semantic Web Work?
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Web Services
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Web services will be greatly improved if
semantics is added to the present Web
resources
Computer will be able to:
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Make doctor appointments
Synchronize with our agenda
Find new suppliers for products we consume
Make travel arrangements
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How Will the Semantic Web Work?
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Applications of Semantic Web
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Personal Agent in Semantic Web
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Responsible for capturing user preferences,
searching for information on available resources,
etc. to provide answer that meet a user’s query
Semantic desktop application
Ontology applications in Art
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Cataloguing online cultural heritage or online
museums
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The Hermitage Museum Web site
www.hermitagemuseum.org
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RDF (Resource Description Framework)
What is RDF?
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RDF stands for Resource Description Framework.
RDF is a framework for describing resources on the
web.
RDF provides a model for data, and a syntax so that
independent parties can exchange and use the data.
RDF is designed to be read and understood by
computers.
RDF is not designed for being displayed to people.
RDF is written in XML.
RDF is a part of the W3C's Semantic Web Activity.
RDF is a W3C Recommendation.
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RDF (Resource Description Framework)
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RDF (Resource Description Framework) is a markup
language for describing information and resources on
the Web.
Putting information into RDF files, makes it possible
for computer programs (“Web spiders") to search,
discover, pick up, collect, analyze, and
process information from the Web.
The Semantic Web uses RDF to describe Web
resources.
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RDF (Resource Description Framework)
RDF Example
The following RDF document could describe the resource
"http://www.w3schools.com/RDF":
The example above is simplified. Namespaces are omitted.
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RDF (Resource Description Framework)
RDF Example
This is a few lines from a CD-list:
This is a few lines of an RDF document:
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RDF (Resource Description Framework)
RDF Example
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The first line of the RDF document is the XML
declaration.
The XML declaration is followed by the root element
of RDF documents: <rdf:RDF>.
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The xmlns:rdf namespace, specifies that elements
with the rdf prefix are from the namespace
"http://www.w3.org/1999/02/22-rdf-syntax-ns#".
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The xmlns:cd namespace, specifies that elements
with the cd prefix are from the namespace
"http://www.recshop.fake/cd#".
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RDF (Resource Description Framework)
RDF Example
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The <rdf:Description> element contains the
description of the resource identified by the
rdf:about attribute.
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The elements: <cd:artist>, <cd:country>,
<cd:company>, etc. are properties of the resource.
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RDF (Resource Description Framework)
How Can It Be Used?
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If information about music, cars, tickets (and
everything else) were stored in RDF files,
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Intelligent Web applications could collect
information from many different sources,
combine the information, and present it to users
in a meaningful way.
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RDF (Resource Description Framework)
How Can It Be Used?
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Information such as:
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Car prices from different resellers
Information about drugs/medications
Flight schedules
Spare parts for the industry
Information about books (price, pages, editor,
year)
Dates of events
Computer updates
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RDF (Resource Description Framework)
RDF - Examples of Use
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Describing properties for shopping items, such as
price and availability
Describing time schedules for Web events
Describing information about Web pages, such as
content, author, creation, and modification date
Describing content and rating for Web pictures
Describing content for search engines
Describing electronic libraries
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Statements and RDF triple
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A basic rule of English grammar is that a complete
sentence (or statement) contains;
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Subject  who or what of the sentence
Predicate  provides information about the subject
Example
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The title of the article is “Computer Science”
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The subject is the article
The predicate is title with a matching value of “Computer
Science”
In RDF, this English statement translates to an
RDF triple
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Statements and RDF triple
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RDF triple
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{ subject, predicate, object }
For example, the statement;
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Ora Lassila is the creator of the resource
http://www.w3.org/home/lassila
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Statements and RDF triple
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The statement can be represented in
RDF as follow;
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Statements and RDF triple
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However, RDF lacks of ability to deal
with relationship between Properties
and Resource
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RDF Schema will helps with this problem
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RDF Schema or RDFS
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The RDF Schema provides the same
functionality as the relational database
schema.
It provides the resources necessary to
describe the objects and properties of a
domain-specific schema, a vocabulary used
to describe objects and their attributes and
relationships within a specific area of
interest.
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RDF Schema or RDFS
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Within the Schema specification, there is a
core group of classes and properties used to
describe domain-specific RDF elements.
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These, combined with a specific set of constrains
RDF Classes
- rdfs:Resource
- rdfs:Class
- rdfs:Literal
- rdfs:XMLLiteral
- rdfs:Datatype
- rdfs:Container
- rdfs:ContainerMembershipProperty
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RDF Schema or RDFS
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RDF Properties
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RDF Schema or RDFS
Ontology of Pests and Crops [Nectec 2005]
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RDF Schema or RDFS
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RDF Schema or RDFS
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Shortcoming of RDF and RDFS
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Local scope of properties
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Disjointness of classes
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rdf:range used to define range of property for every class
Example: property ‘eat’ has a domain ‘animal’ and range ‘meat’,
so every subclass of ‘animal’ will hold this property and cannot
define a new property.
Class ‘male’ and ‘female’ is disjoint class
There is no any instance belongs to both classes
Boolean combination of classes
Cardinality restrictions
Special characteristics of properties
Introducing OWL (Web Ontology Language) … next
week
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Semantic Web Example
Buying and Selling Used Cars
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Suppose a semantic Web system has been built to
administer the selling and buying of used cars
over the Internet.
The system would contain two main applications:
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One for people who want to buy a car
One for people who want to put up a car for sale
Let's call the Internet applications IBA (I Buy
Application) and ISA (I Sell Application).
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Semantic Web Example
IBA - The “I Buy Application”
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People who want to buy a car could use an IBA
application much like this:
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Semantic Web Example
IBA - The “I Buy Application”
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In a "real life" application, you would be asked to
identify yourself the first time you use it.
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Your ID would be stored in an RDF (Resource
Description Framework) file. Your ID would identify you
as a person with name, address, email, and ID number.
When you submitted the query, the application
would return a list of cars for sale and the list could
be drilled down and sorted by year, price, location
and availability.
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This information would be returned from a Web spider
continuously searching the Web for RDF files.
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Semantic Web Example
ISA - The “I Sell Application”
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People who want to sell a car could use an ISA
application much like this:
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Semantic Web Example
ISA - The “I Sell Application”
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When you submit the form, the application would
ask you for more information and store your ID
and the information in an RDF file made available
on the Web.
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The RDF file would contain information such as:
Your ID: Name, address, email, ID number.
Your selling item: type, model, picture, price,
description.
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Semantic Web Example
Behind The Scene
 Behind the scene, the "ISA" application creates an RDF file
with a lot of RDF pointers.
 It creates an RDF pointer to a file with information about
Volvo and Volvo models, an RDF pointer to Volvo dealers
and resellers, about parts, about prices, and much more.
 An RDF pointer is a pointer (actually a URL) to information
about things (like a knowledge database).
The beauty of this is that you don't have to describe
yourself, or the car model. The RDF application will sort it
out for you.
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Semantic Web Example
Will It Ever Work?
 Chaos? Standards? What do we need? What are we
waiting for?
 A standard by W3C, by Microsoft, by Google?
 RDF is data about Web data - or metadata. Often RDF files
describe other RDF files. Will it ever be possible to link all
these RDF files together and build a semantic Web?
 No one knows, but someone will try.
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Semantic Web Example
Will It Work All by Itself?
 The semantic Web will never work all by itself. It
will need some help to become a reality.
 It is not very likely that you will be able to sell
your car just by putting your RDF file on the
Internet.
 The "ISA" and "IBA" applications above will have
to be developed by someone. Someone will
have to build a search engine database for all
the items, and someone will have to develop a
standards for it.
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Semantic Web Example
Will It Work All by Itself?
 It might be eBay, it might be Microsoft, it might
be Google, or someone else. But someone will.
 Soon we will see marketplaces based on RDF.
And one day you will be able to collect
information about almost everything on the Web
in a standardized RDF format.
 It might not be free. You might have to pay for
the information, or at least for selling your
products.
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Conclusion
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SW not only emerges from the Knowledge
Representation and the Web Communities, but also
brings the two communities closer together.
The Software Engineering community can also play
an important role in the development of SW.
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Modeling and verification techniques can be useful at many
stages during the design, maintenance, and deployment of
the Semantic Web ontology.
Complex ontology related properties may not be expressible
within the current Web ontology languages.
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Dong and Dan [Dong and Dan 05] suggested in their study to
use the software engineering techniques and tools for checking
Semantic Web documents.
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Resources
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The World Wide Web Consortium
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The W3 Schools
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http://www.w3schools.com
The WWW Consortium – UK & Ireland
Regional Office
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http://www.w3.org
http://www.w3c.rl.ac.uk
eBay Inc
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http://www.ebay.com
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