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The Semantic Web an introduction. Luigi De Russis. T he Web is a Web of document for people, not for machines. The Semantic Web is a Web of data. Linking Open Data cloud diagram, by Richard Cyganiak and Anja Jentzsch . http://lod-cloud.net/. Let’s think!.

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The semantic web an introduction

The Semantic Web

an introduction

Luigi De Russis


The semantic web an introduction

The Web is a Web of document

for people, not for machines


The semantic web an introduction

The Semantic Web is a Web of data

Linking Open Data cloud diagram,

by Richard Cyganiak and AnjaJentzsch.

http://lod-cloud.net/


The semantic web an introduction

Let’s think!


The semantic web an introduction

Exercise: Build a Music Catalog

Comprehensiveguide to music across the world

Web-based

With always-updated information about each artist


The semantic web an introduction

How?

What are the problems?

What about data replication?

What about data synchronization?

…?


The semantic web an introduction

Solution #1

How?

Site editors roam the Web for new facts and update the site manually

What are the problems?

A lot of people need to continuously roam the Web; the site will get soon out-of-date

What about data?

Data is replicated and not up-to-date with new facts


The semantic web an introduction

Solution #2

How?

Site editors roam the Web for new data and write a program to extract the information

What are the problems?

Code needs to be updated each time a new site is found; the site will get out-of-date, soon or later…

What about data?

Data is replicated and not up-to-date


The semantic web an introduction

Solution #3

How?

Site editors browse the Web for new data via APIs, and write some code to incorporate the information

What are the problems?

Code needs to be updated each time a new site is found and/or an API is changed; the site will get out-of-date, soon or later…

What about data?

Data is replicated and not up-to-date


The semantic web an introduction

Solution #4

How?

Site editors choose to use some external, public datasets (e.g., Wikipedia, MusicBrainz, …)

What are the problems?

No problem

What about data?

Data is immediately available, not as APIs or hidden on a Web site. Information can be extracted using standard queries or HTTP requests.


The semantic web an introduction

Solution #4

In short…

Use the Web of Data as a Content Management System

Use the community at large as content editor

An example: BBC Music

http://www.bbc.co.uk/music


The semantic web an introduction

Data on the Web is not enough!

we need a proper infrastructure

Data should be available on the Web

accessible via standard Web technologies

Data should be interlinked over the Web

i.e., data can be integrated over the Web

This is where Semantic Web come in


The semantic web an introduction

Fundamentals


The semantic web an introduction

To a computer, the Web is a flat, boring world, devoid of meaning. This is a pity, as in fact documents on the Web describe real objects and imaginary concepts. […]

Adding semantics to the Web involves two things: allowing documents which have information in machine-readable forms, and allowing links to be created with relationship values. Only when we have this extra level of semantics we will be able to use computer power to help us exploit the information to a greater extent than our own reading.

Tim Berners-Lee, 1994


The semantic web an introduction

What is the relationship with AI?

Influence

Some technologies in the Semantic Web benefited a lot from AI research and development (and viceversa)

Different goals

Artificial Intelligence approach: build smarter machines, teach computers to infer the meaning of data

Semantic Web approach: have smarter data, make data easier for machines to find, access and process


The semantic web an introduction

Resource and description

Resource

every document “reachable” on the Web

no matter the content, format, language, etc.

Resource description

independent from the format

standard language (metadata)


The semantic web an introduction

Resource and description

Resources


The semantic web an introduction

Resource and description

Description


The semantic web an introduction

Resource and description

Title

Author

Date

Topic

Quality

Description

TitleAuthor

DateTopic


The semantic web an introduction

URIs

unambiguousnames for resources

RDF

a common data model to connectand describe resources

SPARQL

access to the data model

RDFS, OWL

common description languages

OWL, RIF

reasoning (mainly logic inference)


The semantic web an introduction

Modeling Data


The semantic web an introduction

Example: bookstore

Represent the following data about the AI book as a set of relations

Title: “Artificial Intelligence: A Modern Approach”

Author:Russel, Stuart and Norvig, Peter

Publisher: Prentice Hall

ISBN: 978-0136042594


The semantic web an introduction

Example: bookstore

http://...isbn/9780136042594

Resource


The semantic web an introduction

Example: bookstore

http://...isbn/9780136042594

Artificial Intelligence: A Modern Approach

Literal


The semantic web an introduction

Example: bookstore

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach


The semantic web an introduction

Example: bookstore

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach

publisher

author

Prentice Hall

author

Norvig, Peter

Russel, Stuart


The semantic web an introduction

RDF: Resource Description Framework

Structured in statements

Subject

a resource (URI)

Predicate

a verb, property or relationship

Object

a resource or a literal string


The semantic web an introduction

Example: bookstore

Object

Subject

Predicate

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach

Predicate

Predicate

publisher

Object

author

Prentice Hall

Object

author

Norvig, Peter

Object

Russel, Stuart


The semantic web an introduction

Example: bookstore

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach

RDF in XML syntax

<rdf:RDFxmlns:rdf=http://www.w3.org/…/22-rdf-syntax-ns#>

<rdf:Descriptionabout=“http://... isbn/9780136042594”>

<title>Artificial Intelligence: A Modern Approach</title>

</rdf:Description>

</RDF>


The semantic web an introduction

Example: bookstore

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach

RDF in Turtle

<http://... isbn/9780136042594>

title “Artificial Intelligence: A Modern Approach”


The semantic web an introduction

Linkin’ Data


The semantic web an introduction

Example: bookstore

Represent the following data about the Italian translation of the AI book as a set of relations

Title: “Intelligenzaartificiale. Un approcciomoderno”

Author:Russel, Stuart and Norvig, Peter

Publisher: Prentice Hall

ISBN: 978-8871925936

Original ISBN: 978-0136042594


The semantic web an introduction

Example: bookstore

IntelligenzaArtificiale. Un approcciomoderno

title

http://...isbn/9788871925936

publisher

original

Prentice Hall

http://...isbn/9780136042594

creator

creator

Russel, Stuart

Norvig, Peter


The semantic web an introduction

Example: bookstore

IntelligenzaArtificiale. Un approcciomoderno

title

http://...isbn/9788871925936

publisher

Prentice Hall

original

http://...isbn/9780136042594

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach

publisher

Prentice Hall


The semantic web an introduction

Example: bookstore

IntelligenzaArtificiale. Un approcciomoderno

title

http://...isbn/9788871925936

publisher

Prentice Hall

original

http://...isbn/9780136042594

same URI, same resource

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach

Prentice Hall

creator


The semantic web an introduction

Example: bookstore

IntelligenzaArtificiale. Un approcciomoderno

title

http://...isbn/9788871925936

publisher

Prentice Hall

original

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach

publisher

author

creator

Prentice Hall

creator

Russel, Stuart

Norvig, Peter

author

Russel, Stuart

Norvig, Peter


The semantic web an introduction

Example: bookstore

IntelligenzaArtificiale. Un approcciomoderno

title

http://...isbn/9788871925936

What about merging creator and author?

In RDF, it is not possible!

publisher

Prentice Hall

original

http://...isbn/9780136042594

title

Artificial Intelligence: A Modern Approach

publisher

author

creator

Prentice Hall

creator

Russel, Stuart

Norvig, Peter

author

Russel, Stuart

Norvig, Peter


The semantic web an introduction

Problem: field names are arbitrary

Synonyms : author or creator or maker or contributor or…

Singular or plural: author or authors

Solution: standards

general or domain-specific


The semantic web an introduction

Dublin Core

General vocabulary

Dublin Core Metadata Initiative (DCMI)

http://dublincore.org

Building blocks to define metadata for the Semantic Web

Define title, contributor, publisher, license, date, language, etc.


The semantic web an introduction

Problem: field values are arbitrary

Value type: string, date, integer, …

Value format: “Norvig, Peter” or “Norvig, P.” or “Peter Norvig” or…

Value restrictions: one value or multiple values (how many?)

Solutions

Standards

Controlled vocabulary (close list of terms)

Semantically rich descriptions to support search (RDFS and/or OWL)


The semantic web an introduction

Friend Of A Friend (FOAF)

General ontology

Describe persons, their activities and their relations to other people and objects

http://www.foaf-project.org

Building blocks to define structured relations between people

Define name, familyName, givenName, knows, age, nick, etc.


The semantic web an introduction

Example: bookstore

http://...isbn/9780136042594

dc:title

Artificial Intelligence: A Modern Approach

dc:publisher

dc:creator

dc:creator

foaf:name

Prentice Hall

foaf:name

foaf:name

Norvig, Peter

Russel, Stuart

foaf: http://xmlns.com/foaf/spec

dc: http://purl.org/dc/terms


The semantic web an introduction

Why?

http://...isbn/9780136042594

http://...isbn/9780136042594

dc:creator

author

foaf:name

Norvig, Peter

Norvig, Peter


The semantic web an introduction

RDF Schema


The semantic web an introduction

RDF Schema

Schema

Definition of the nodes and predicates used in a RDF document

Domainand Range

RDFS describes properties in terms of classes of resource

to which they apply (from a “domain” to a “range”)


The semantic web an introduction

Example

RDF data

http://elite.polito.it/people/derussis

http.//bit.ly/lingambmult

teaches


The semantic web an introduction

Example

Person

subClassOf

domain

range

Teacher

Course

teaches

type

type

RDF schema

RDF data

http://elite.polito.it/people/derussis

http.//bit.ly/lingambmult

teaches


The semantic web an introduction

Back to the bookstore example…

http://...isbn/9780136042594

http://...isbn/9780136042594

dc:creator

Why?

author

foaf:name

Norvig, Peter

Norvig, Peter


The semantic web an introduction

Back to the bookstore example…

http://...isbn/9780136042594

http://...isbn/9780136042594

dc:creator

Why?

anonymous

class

author

foaf:name

Norvig, Peter

Norvig, Peter

dc:creator has range Agent, i.e. a class (resource), not a literal:

we use an anonymous class for this scope.

Finally, foaf:Name has range rdfs:Literal.


The semantic web an introduction

RDFS Expressivity

  • Simple relationship between things

  • RDFS provides a vocabulary to express relationship between things (e.g., subClassOf or type)

  • Avoid complex relationship

  • RDFS cannot describe data in terms of set of operations (e.g., unionOf), equivalence (e.g., sameAs) or cardinality (e.g., allValueFrom)


The semantic web an introduction

OWL


The semantic web an introduction

Web Ontology Language

What?

OWL (version 2): a knowledge representation language

Designed to formulate, exchange and reason with knowledge about a domain of interest


The semantic web an introduction

Web Ontology Language

Individuals, classes and properties

“Politecnico di Torino is a university”

“Politecnico di Torino has a professor named Elio Piccolo”

“Politecnico di Torino” is a object: an individual in OWL2

“university” is a category: a class in OWL2

“has a professor” is a relation: a property in OWL2

“Elio Piccolo” is an individual, too


The semantic web an introduction

Web Ontology Language

Expressivity

Designed to represent rich and complex knowledge about things, group of things, and their relations

Logic-based

Knowledge expressed in OWL can be reasoned with a computer program to verify its consistency or to make implicit knowledge explicit


The semantic web an introduction

Web Ontology Language

Linked

Ontologies in OWL can be published on the Web and may refer or be referred from other OWL ontologies

Choose the syntax you like

Various syntaxes available for OWL, for different purposes

(RDF/XML, Turtle, Manchester, etc.)


The semantic web an introduction

Example: bookstore

dc:title

IntelligenzaArtificiale. Un approcciomoderno

http://...isbn/9788871925936

rdfs:type

dc:publisher

Prentice Hall

Libro

owl:sameAs

Book

rdf:type

Artificial Intelligence: A Modern Approach

dc:title

http://...isbn/9780136042594

Prentice Hall

dc:publisher


The semantic web an introduction

Hands on OWL


The semantic web an introduction

Example: Bookstore

It is time to sell the books we modeled.

Users must have the possibility to search in our book catalog.

We need to describe our store

and add some other information about the books.

GoodRelations helps in realizing such an example:

http://www.heppnetz.de/projects/goodrelations/


The semantic web an introduction

“EUR”

gr:hasCurrency

120.0

1.0

gr:amountOfThisGood

gr:Sell

gr:hasCurrencyValue

TypeAndQuantityNode_1

UnitPriceSpecification_1

gr:hasBusinessFunction

gr:hasPriceSpecification

gr:typeOfGood

Offering_1

gr:includeObject

AIBook_en

Bookstore_1

gr:offers

rdf:type

gr:Offering

rdf:type

item:hasTotalPages

item:Book

QuantitativeValueInteger_1

rdf:type

rdfs:subClassOf

gr:hasValue

gr:ActualProductOrServiceInstance

gr:ProductOrService

1132


The semantic web an introduction

Describe the business entity

Bookstore_1

default:BookStore_1

a gr:BusinessEntity ;

gr:legalName “bookstore.com Ltd.”^^xsd:string .


The semantic web an introduction

Describe the offered items

AIBook_en

default:AIBook_en

a item:Book, gr:ActualProductOrServiceInstance ;

item:hasTotalPagesdefault:QuantitativeValueInteger_1 .

QuantitativeValueInteger_1

default:QuantitativeValueInteger_1

a gr:QuantitativeValueInteger ;

gr:hasValue “1132”^^xsd:integer .


The semantic web an introduction

Describe the offer

Offering_1

default:Offering_1

a gr:Offering ;

gr:hasBusinessFunctiongr:Sell ;

gr:hasPriceSpecification default:UnityPriceSpecification_1 ;

gr:includeObject default:TypeAndQuantityNode_1 .

Link the offer to the business entity

default:BookStore_1 gr:offers default:Offering_1


The semantic web an introduction

Describe the offer

TypeAndQuantityNode_1

default:TypeAndQuantityNode_1

a gr:TypeAndQuantityNode ;

gr:amountOfThisGood “1.0”^^xsd:float ;

gr:typeOfGooddefault:AIBook_en .

UnitPriceSpecification_1

default:UnitPriceSpecification_1

a gr:UnitPriceSpecification ;

gr:hasCurrency “EUR”^^xsd:string ;

gr:hasCurrencyValue “120.0”^^xsd:float .


The semantic web an introduction

Query the whole!

How to get all the available offer for the book?

SPARQL

PREFIX gr: <http://purl.org/goodrelations/v1#>

PREFIX item: <http://www.elite.polito.it/ontologies/example/item#>

SELECT ?offering

WHERE { ?offering rdf:typegr:Offering .

?offering gr:includesObject ?object .

?object gr:typeOfGood ?item .

?item rdf:typeitem:Book .

}


The semantic web an introduction

Query the whole!

SPARQL

?item rdf:typeitem:Book .

?item

rdf:type

item:Book


The semantic web an introduction

Query the whole!

SPARQL

?object gr:typeOfGood ?item .

?object

gr:typeOfGood

AIBook_en

rdf:type

item:Book


The semantic web an introduction

Query the whole!

SPARQL

?offering gr:includesObject ?object .

TypeAndQuantityNode_1

gr:typeOfGood

?offering

gr:includeObject

AIBook_en

rdf:type

item:Book


The semantic web an introduction

Query the whole!

SPARQL

?offering rdf:typegr:Offering .

TypeAndQuantityNode_1

gr:typeOfGood

?offering

gr:includeObject

AIBook_en

rdf:type

rdf:type

gr:Offering

item:Book


The semantic web an introduction

Query the whole!

SPARQL

SELECT ?offering

TypeAndQuantityNode_1

?offering

gr:typeOfGood

Offering_1

gr:includeObject

AIBook_en

rdf:type

rdf:type

gr:Offering

item:Book


The semantic web an introduction

References

Semantic Web standards: http://w3c.org/standards/semanticweb

Semantic Web Wiki: http://semanticweb.org

Semantic Web FAQ: http://www.w3c.org/2001/sw/SW-FAQ

Book: A Semantic Web Primer (http://www.semanticwebprimer.org)

Book: Semantic Web Programming (http://semwebprogramming.org)

Last access: 04 June 2013


The semantic web an introduction

Thanks!

Luigi De Russis

http://elite.polito.it


The semantic web an introduction

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