Semantic Web and Ontologies

Semantic Web and Ontology:What, Why and How

Manu Madhavan

Asst.Professor,Dept. of Computer Science and Engg.

Sreepathy Institute of Management And [email protected]

7 Oct, 2013.

Manu Madhavan Semantic Web and Ontologly

Let us start


Are you satisfied with current search ?

Does Googling always give you required results?

Do you thing current web services are enough for your works?

what you require otherwise ?


What Stops Us From Doing More?

Traditional Web is entirely aimed for reading and is purelydisplay oriented.

HTML Tags doesn’t carry any information about the content

Search is merely keyword matching. Page ranking does notconsider the context.

Computers can only present users with information, but theycannot “understand” the information well enough to displaythe data that is most relevant in a given circumstance.


Think a minute....

Whether it is possible to reconstruct the Web by adding someinformation into the documents stored on the Internet so that thecomputers can use this extra information to understand what agiven document is really about? YES !!! Solution is Semantic

Web


Think a minute....

Whether it is possible to reconstruct the Web by adding someinformation into the documents stored on the Internet so that thecomputers can use this extra information to understand what agiven document is really about?

YES !!! Solution is Semantic Web


Semantic Web

The Semantic Web is an extension of the current Web inwhich information is given well-defined meaning, betterenabling computers and people to work in cooperation.

Tim Berners–Lee

The Semantic Web is not about links between web pages. Itdescribes the relationships between things (like A is a part ofB and Y is a member of Z) and the properties of things (likesize, weight, age, and price)

W3School


How to add semantics to the web ?

The simplest way is provide more information: as Metadata:Data About Data

Then use a special Crawler (search agent) to look themetadata for more information.


Semantic Search ?

Build a common vocabulary:a commonly accepted name for this common vocabulary file isontology

Mark up the web pages with semantics ( use XML and highermarkups)

Build an intelligent crawler ( use NLP techniques)


Semantic Web Architecture


Building Blocks

Ontology

Resource Description Frame Work (RDF)

Web Ontology Language (OWL)

Reasoners


Ontology

Common vocabulary is represented as Ontology

Representation of Shared conceptualization

Represent relations between entities/ resources

Domain Specific


Resource Description Frame Work

RDF is a language for describing information and resources onthe web.

RDF is structured; i.e., it is machine-understandable.

RDF is an XML-based language for describing informationcontained in a Web resource.

The three main components are: RESOURCE, PROPERTY,and STATEMENT


RDF: Resource

Resource is anything that is being described by RDFexpressions

The name of a resource must be global.

Resource is located by a URI

URI have namespace + “#′′ + localResourceName

eg: www .simplegroups.in/ontoClass#Book .


RDF: Property

Property is a resource that has a name and can be used as aproperty

It can be used to describe some specific aspect, characteristic,attribute, or relation of the given resource.

URI have namespace + “#′′ + PropertyName

eg: www .simplegroups.in/ontoClass#hasAuthor .


RDF: Statement

An RDF statement is used to describe properties of resources.

resource (subject) + property (predicate) + property value(object)

〈subject〉 has a property 〈predicate〉, whose value is 〈object〉eg: 〈www .simplegroups.in/ontoClass/Book#ANSI C 〉〈www .simplegroups.in/ontoClass#hasAuthor〉〈www .simplegroups.in/ontoClass/person#Balagurswami〉 .


RDF Document Example


Web Ontology Language

OWL = RDF schema + new constructs for expressiveness

OWL build on RDF, with more features to express thesemantics

Semantics is expressed by adding restrictions, class- sub classrelations, cardinality constrains, etc.

The properties can be further expressed as symmetric,transitive, equivalent, inverse etc of other properties.

OWL available in 3 forms: OWL -Lite, OWL - DL and OWL-Full


Reasoners

infer logical consequences from a set of asserted facts oraxioms.

Add OWL property features: inverseOf, sameAs,

subpropertyOf, etc.

e.g.

Event hasBirthDate Dateand hasEvent inversOf hasBirhtDate

Then a reasoner will add:

Date hasEvent Event

Pellet Reasoner is used.


Example: Building an Ontology

Consider the example: [an extract from Wikipedia article aboutSachin Tendulkar, 06-Oct-2013.] .

Tendulkar was born at Nirmal Nursing Home on 24 April

1973. His father Ramesh Tendulkar was a reputed

Marathi novelist and his mother Rajni worked in the

insurance industry. Ramesh named Tendulkar after his

favorite music director, Sachin Dev Burman.


Creating Base Ontology

Identify domain entities

In the example document, Birth, Play, Person, Date,Location

Identify events and relations between events and entities

Person hasEvent Birth

Birth hasBirthDate Date

Birth hasBirthLocation Location


Creating Base Ontology

Figure: Base Ontology Graph


Implementing Base Ontology: Classes

Figure: OWL Representation


Implementing Base Ontology: Properties

Figure: Properties


Implementing Base Ontology: Adding instances

Figure: Populating Ontology


Open source Tools for Ontology

SWOOP :Ontology Editor, Viewer and Reasoner (Demo)

Protege : Ontology Editor, Viewer and Reasoner

Jena- API: To Create ontology programmatically

Python-RDFLib package can be used for Ontologyapplications (with python)


Jena API

Java API for ontology applications.

It will first create a OWL base ontology model and then addfeatures to this model object.

Model model=ModelFactory.createDefaultModel();OntClass Person=model.addClass(“PERSON”);OntClass Event=model.addClass(“EVENT”);OntClass Birth=model.addClass(“BIRTH”);Event.addSubClass(Birth);ObjectProperty hasBirthDate =

model.addObjectTypeProperty(“hasBirthDate”);hasBirthDate.addDomain(Event);hasBirthDate.addRange(Date);


Conclusion

Semantic Web is an extension to traditional web with moreinformation to machine understandability.

Ontology, RDF and OWL are the three main components ofSemantic Web

Tools like SWOOP, Protege, Jena etc can be used forontology development.

Reasoners are used to infer implicit knowledge from theOntologly.


Open Discussion


Semantic Web and Ontologies

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