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Introduction to Semantic Web

Teeratorn SaneeyengDepartment of Computer EducationKing Mongkut’s University of Technology North Bangkok

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Outline Background Semantic Web

Definitions How Will the Semantic Web Work?

Ontologies RDF (Resource Description Framework) Semantic Web Examples Conclusion

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Background Human are capable of using the Web to carry out

tasks such as; 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; Web pages are designed to be read by human, not

machines

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Background 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 Semantic Web will overcome such the

problems by making the Web not only human-understandable but also machine-understandable.

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 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 It derives from W3C1 director Sir Tim Berners-Lee's

vision of the Web as a universal medium for data, information, and knowledge exchange.

The word semantics stand for the meaning of. The semantics of something is the meaning of something.

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) 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?

This is what the Semantic Web is all about: 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)

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].

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? Knowledge Management

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]: 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) 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: 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) Web Commerce

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) 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 up-to-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? 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. 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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TechnologiesApplications

Concepts

SemanticWeb

• Metadata• Ontologies• Ontology Languages• Web Services

Themes related to the Semantic Web [Breitman et al. 07]

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Metadata 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

How Will the Semantic Web Work?

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Ontologies In computer science, ontologies were

adopted in AI to facilitate knowledge sharing and reuse [Fensel 01]

Becoming widespread in areas: Intelligent information integration Cooperative information systems Agent-based software engineering E-commerce

How Will the Semantic Web Work?

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Ontologies

Sample ontology of a Computer Science Department [Doan et al. 03]

How Will the Semantic Web Work?

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Ontology Languages Designed to define ontologies They are sometimes called:

Lightweight ontology languages Web-based ontology languages Markup ontology languages

RDF (Resource Description Language) OWL (Web Ontology Language)

How Will the Semantic Web Work?

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Web Services Web services will be greatly improved if

semantics is added to the present Web resources

Computer will be able to: Make doctor appointments Synchronize with our agenda Find new suppliers for products we consume Make travel arrangements

How Will the Semantic Web Work?

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Applications of Semantic Web Personal Agent in Semantic Web

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

Cataloguing online cultural heritage or online museums The Hermitage Museum Web site

www.hermitagemuseum.org

How Will the Semantic Web Work?

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RDF (Resource Description Framework)What is RDF? 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) 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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The example above is simplified. Namespaces are omitted.

RDF (Resource Description Framework)RDF Example

The following RDF document could describe the resource "http://www.w3schools.com/RDF":

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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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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>.

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#".

The xmlns:cd namespace, specifies that elements with the cd prefix are from the namespace "http://www.recshop.fake/cd#".

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.

The elements: <cd:artist>, <cd:country>, <cd:company>, etc. are properties of the resource.

RDF (Resource Description Framework)RDF Example

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RDF (Resource Description Framework)How Can It Be Used?

If information about music, cars, tickets (and everything else) were stored in RDF files, 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?

Information such as: 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 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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A basic rule of English grammar is that a complete sentence (or statement) contains; Subject who or what of the sentence Predicate provides information about the subject

Example The title of the article is “Computer Science”

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

Statements and RDF triple

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RDF triple { subject, predicate, object } For example, the statement;

Ora Lassila is the creator of the resource http://www.w3.org/home/lassila

Statements and RDF triple

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Statements and RDF triple

The statement can be represented in RDF as follow;

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Statements and RDF triple

However, RDF lacks of ability to deal with relationship between Properties and Resource RDF Schema will helps with this problem

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RDF Schema or RDFS

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

Within the Schema specification, there is a core group of classes and properties used to describe domain-specific RDF elements. 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

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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Shortcoming of RDF and RDFS Local scope of properties

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.

Disjointness of classes 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

RDF Schema or RDFS

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Semantic Web Example

Buying and Selling Used Cars

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: 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”

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”

In a "real life" application, you would be asked to identify yourself the first time you use it. 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. 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”

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”

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.

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 waitin

g 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 yo

ur 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 b

e Google, or someone else. But someone will. Soon we will see marketplaces based on RDF. A

nd 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 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. 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. 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

The World Wide Web Consortium http://www.w3.org

The W3 Schools http://www.w3schools.com

The WWW Consortium – UK & Ireland Regional Office http://www.w3c.rl.ac.uk

eBay Inc http://www.ebay.com