Semantic Web: an introduction

THE SEMANTIC WEB AN INTRODUCTION

LUIGI DE RUSSIS

THE 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!

EXERCISE: BUILD A MUSIC CATALOG

Comprehensive guide to music across the world

Web-based

With always-updated information about each artist

HOW?

WHAT ARE THE PROBLEMS?

WHAT ABOUT DATA REPLICATION?

WHAT ABOUT DATA SYNCHRONIZATION?

…?

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soon out-of-date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

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out-of-date, soon or later…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

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changed; the site will get out-of-date, soon or later…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

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.

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

SOLUTION #4

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

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

FUNDAMENTALS

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

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

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)


Resources


Description


Description Title

Author

Date

Topic

Quality

Title Author

Date Topic

URIS unambiguous names for resources

RDF a common data model to connect and describe resources

SPARQL access to the data model

RDFS, OWL common description languages

OWL, RIF reasoning (mainly logic inference)

MODELING DATA

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

EXAMPLE: BOOKSTORE

http://...isbn/9780136042594

Resource

EXAMPLE: BOOKSTORE

http://...isbn/9780136042594 Artificial Intelligence: A Modern

Approach

Literal

EXAMPLE: BOOKSTORE


Approach

title

EXAMPLE: BOOKSTORE


Approach

Prentice Hall

Russel, Stuart

Norvig, Peter

title

publisher

author

author

RDF: RESOURCE DESCRIPTION FRAMEWORK

STRUCTURED IN STATEMENTS

SUBJECT a resource (URI)

PREDICATE a verb, property or relationship

OBJECT a resource or a literal string

EXAMPLE: BOOKSTORE


Approach

Prentice Hall

Russel, Stuart

Norvig, Peter

title

publisher

author

author

Subject Object

Object

Object

Object

Predicate Predicate

Predicate

EXAMPLE: BOOKSTORE


Approach

title

RDF IN XML SYNTAX

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

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

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

</rdf:Description>

</RDF>

EXAMPLE: BOOKSTORE


Approach

title

RDF IN TURTLE

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

title “Artificial Intelligence: A Modern Approach”

LINKIN’ DATA

EXAMPLE: BOOKSTORE

Represent the following data about the Italian translation of the AI book

as a set of relations

Title: “Intelligenza artificiale. Un approccio

moderno”

Author: Russel, Stuart and Norvig, Peter

Publisher: Prentice Hall

ISBN: 978-8871925936

Original ISBN: 978-0136042594

EXAMPLE: BOOKSTORE

http://...isbn/9788871925936

Intelligenza Artificiale. Un

approccio moderno

Prentice Hall

Russel, Stuart

Norvig, Peter

title

publisher

creator creator

http://...isbn/9780136042594

original

EXAMPLE: BOOKSTORE

http://...isbn/9788871925936


approccio moderno

Prentice Hall

title

publisher

http://...isbn/9780136042594

original


Approach

Prentice Hall

title

publisher

EXAMPLE: BOOKSTORE

http://...isbn/9788871925936


approccio moderno

Prentice Hall

title

publisher

http://...isbn/9780136042594

original


Approach

Prentice Hall

title

creator

same URI, same resource

EXAMPLE: BOOKSTORE


Approach

Prentice Hall Russel, Stuart

Norvig, Peter

title

publisher

author

author

http://...isbn/9788871925936


approccio moderno

Prentice Hall

title

publisher

original

Russel, Stuart

Norvig, Peter

creator

creator

EXAMPLE: BOOKSTORE


Approach

Prentice Hall Russel, Stuart

Norvig, Peter

title

publisher

author

author

http://...isbn/9788871925936


approccio moderno

Prentice Hall

title

publisher

original

Russel, Stuart

Norvig, Peter

creator

creator

What about merging creator and author?

In RDF, it is not possible!

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

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.

http://dublincore.org/

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)

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.

http://www.foaf-project.org/



EXAMPLE: BOOKSTORE


Approach

Prentice Hall

Russel, Stuart

Norvig, Peter

dc:title

dc:publisher dc:creator

dc:creator

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

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

foaf:name

foaf:name

foaf:name

http://...isbn/9780136042594

Norvig, Peter

dc:creator

foaf:name

http://...isbn/9780136042594

Norvig, Peter

author

WHY?

RDF SCHEMA

RDF SCHEMA

SCHEMA Definition of the nodes and predicates used in a RDF document

DOMAIN AND RANGE RDFS describes properties in terms of classes of resource

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

EXAMPLE

RDF data

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

http.//bit.ly/lingambmult

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

EXAMPLE

RDF data

RDF schema

http.//bit.ly/lingambmult

Teacher

Person

teaches Course

domain range

subClassOf

type type

http://...isbn/9780136042594

Norvig, Peter

dc:creator

foaf:name

http://...isbn/9780136042594

Norvig, Peter

author

BACK TO THE BOOKSTORE EXAMPLE…

http://...isbn/9780136042594

Norvig, Peter

dc:creator

foaf:name

http://...isbn/9780136042594

Norvig, Peter

author

BACK TO THE BOOKSTORE EXAMPLE…

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.

anonymous

class

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)

OWL

WEB ONTOLOGY LANGUAGE

WHAT? OWL (version 2): a knowledge representation language

Designed to formulate, exchange and reason with knowledge about a

domain of interest


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


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


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.)

EXAMPLE: BOOKSTORE Intelligenza Artificiale. Un

approccio moderno

Prentice Hall

dc:title

dc:publisher

Artificial Intelligence: A Modern

Approach

Prentice Hall

dc:title

dc:publisher

Libro

Book

rdfs:type

rdf:type

owl:sameAs

http://...isbn/9788871925936

http://...isbn/9780136042594

HANDS ON OWL

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/




Bookstore_1

Offering_1

TypeAndQuantity

Node_1 UnitPriceSpecification_1

AIBook_en

item:Book QuantitativeValue

Integer_1

gr:Sell

120.0

“EUR”

1.0

1132 gr:ActualProductOrServiceInstance

gr:ProductOrService

gr:offers

gr:includeObject

gr:hasBusinessFunction

gr:hasPriceSpecification

gr:hasCurrency

gr:hasCurrencyValue gr:amountOfThisGood

gr:typeOfGood

rdf:type

rdfs:subClassOf

rdf:type

item:hasTotalPages

gr:hasValue

gr:Offering

rdf:type

DESCRIBE THE BUSINESS ENTITY

default:BookStore_1

a gr:BusinessEntity ;

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

Bookstore_1

DESCRIBE THE OFFERED ITEMS

default:AIBook_en

a item:Book, gr:ActualProductOrServiceInstance ;

item:hasTotalPages default:QuantitativeValueInteger_1 .

AIBook_en

default:QuantitativeValueInteger_1

a gr:QuantitativeValueInteger ;

gr:hasValue “1132”^^xsd:integer .

QuantitativeValue

Integer_1

DESCRIBE THE OFFER default:Offering_1

a gr:Offering ;

gr:hasBusinessFunction gr:Sell ;

gr:hasPriceSpecification default:UnityPriceSpecification_1 ;

gr:includeObject default:TypeAndQuantityNode_1 .

Offering_1

LINK THE OFFER TO THE BUSINESS ENTITY default:BookStore_1 gr:offers default:Offering_1

DESCRIBE THE OFFER

default:TypeAndQuantityNode_1

a gr:TypeAndQuantityNode ;

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

gr:typeOfGood default:AIBook_en .

default:UnitPriceSpecification_1

a gr:UnitPriceSpecification ;

gr:hasCurrency “EUR”^^xsd:string ;

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

TypeAndQuantity

Node_1

UnitPriceSpecification_1

QUERY THE WHOLE!

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

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

SELECT ?offering

WHERE { ?offering rdf:type gr:Offering .

?offering gr:includesObject ?object .

?object gr:typeOfGood ?item .

?item rdf:type item:Book .

}

How to get all the available offer for the book?

SPARQL

QUERY THE WHOLE!

?item rdf:type item:Book . SPARQL

?item

item:Book

rdf:type

QUERY THE WHOLE!

?object gr:typeOfGood ?item . SPARQL

?object

AIBook_en

item:Book

gr:typeOfGood

rdf:type

QUERY THE WHOLE!

?offering gr:includesObject ?object . SPARQL

?offering

TypeAndQuantity

Node_1

AIBook_en

item:Book

gr:includeObject

gr:typeOfGood

rdf:type

QUERY THE WHOLE!

?offering rdf:type gr:Offering . SPARQL

?offering

TypeAndQuantity

Node_1

AIBook_en

item:Book

gr:includeObject

gr:typeOfGood

rdf:type gr:Offering

rdf:type

QUERY THE WHOLE!

SELECT ?offering SPARQL

Offering_1

TypeAndQuantity

Node_1

AIBook_en

item:Book

gr:includeObject

gr:typeOfGood

rdf:type gr:Offering

rdf:type

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

http://w3c.org/standards/semanticweb

http://semanticweb.org/

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



http://www.semanticwebprimer.org/

http://semwebprogramming.org/

THANKS!

Luigi De Russis

http://elite.polito.it

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Semantic Web: an introduction

Technology

data replication

data synchronization

modeling data

web of documentfor people

russ prenticehallisbn

richard cyganiak

imaginary concepts

boring world