The Semantic Web a short guide

 Maciej  Dabrowski  macdab@gmail.com  

THE SEMANTIC WEB

WHAT IS THE GOAL?

WHAT ARE THE BUILDING BLOCKS?

HOW DO WE CREATE THE GRAPH?

WHY LINKED DATA?

SHORT INTRO TO ONTOLOGIES

What’s in a page ? And in a link ?

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VISION FOR THE WEB

TIM BERNERS-LEE, THE 1ST WORLD WIDE WEB CONFERENCE, GENEVA, MAY 1994:

DESCRIBE DOCUMENTS IN MACHINE READIBLE FORM CREATE MEANINGFUL LINKS (“RELATIONSHIP VALUES”) “ONLY WHEN WE HAVE THIS EXTRA LEVEL OF SEMANTICS

WILL WE BE ABLE TO USE COMPUTER POWER TO HELP US EXPLOIT THE INFORMATION TO A GREATER EXTENT THAN OUR OWN READING.”

Aims of the Semantic Web

BRIDGING THE GAP BETWEEN A WEB OF DOCUMENTS TO A WEB OF DATA, WITH TYPED OBJECTS AND TYPED RELATIONSHIPS ADDING MACHINE-READABLE METADATA TO EXISTING CONTENT, SO THAT INFORMATION CAN BE PARSED, QUERIED, REUSED

Aims of the Semantic Web

DEFINING SHARED SEMANTICS FOR THIS METADATA TO ALLOW INTEROPERABILITY BETWEEN APPLICATIONS AND FOR ADVANCED PURPOSES, SUCH AS REASONING ENABLING MACHINE-READABLE KNOWLEDGE AT WEB SCALE, MAKING INFORMATION MORE EASY TO FIND AND PROCESS

The Semantic Web, circa 2010

MOST STANDARDISATION WORK IS DONE IN THE W3C:

HTTP://WWW.W3.ORG/

INCUBATOR GROUPS, WORKING GROUP, INTEREST GROUPS:

WGS FOR SPARQL, RDB2RDF, RIF, ETC. HCLS IG, SOCIAL WEB XG, ETC.

Name everything

Identifying resources with URIs

URIS ARE USED TO IDENTIFY EVERYTHING IN A UNIQUE AND NON-AMBIGUOUS WAY NOT ONLY PAGES (AS ON THE CURRENT WEB), BUT ANY RESOURCE (PEOPLE, DOCUMENTS, BOOKS, INTERESTS, ETC.) A URI FOR A PERSON IS DIFFERENT FROM A URI FOR A DOCUMENT ABOUT THE PERSON, BECAUSE A PERSON IS NOT A DOCUMENT! e.g. http://deri.ie/user/maciej-dabrowski

e.g. http://deri.ie/content/modelling-preference-relaxation-e-commerce

Defining assertions with RDF

•  URIS IDENTIFY RESOURCES: •  WE USE RDF (RESOURCE DESCRIPTION

FRAMEWORK) TO DEFINE ASSERTIONS ABOUT THESE RESOURCES

•  RDF IS A DATA MODEL; A DIRECTED, LABELED GRAPH USING URIS

•  RDF IS BASED ON TRIPLES: – <SUBJECT> <PREDICATE> <OBJECT>.!

Simple triples

Maciej Dabrowski

MDabrowski-lecture3

author

Semantic_Web

Introduction to the Semantic Web

title

subject

Use Uris

http://example.org/maciej-dabrowski

http://example.org/MDabrowski-lecture3

http://example.org/author

http://example.org/Semantic_Web

Introduction to the Semantic Web

http://example.org/title

http://example.org/subject

Abbreviating uris

PREFIX ex: http://example.org/# ex:maciej = <http://example.org/#maciej>

ex:maciej-dabrowski

ex:MDabrowski-lecture3

ex:author

ex:Semantic_Web

Introduction to the Semantic Web

ex:title

ex:subject

Reuse existing vocabularies

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

http://deri.ie/user/maciej-dabrowski

http://example.org/MDabrowski-lecture3

dct:creator

http://dbpedia.org/resource/Semantic_Web

Introduction to the Semantic Web

dct:title

dct:subject

RDF by example !!@prefix dct: <http://purl.org/dc/terms/> . !<http://example.org/dm110-semweb>!!dct:title “Introduction to the Semantic Web” ; !

!dct:author <http://www.deri.ie/users/maciej-dabrowski> ; !!!dct:subject <http://dbpedia.org/resource/Semantic_Web> .!

RDFA

A WAY OF EMBEDDING RDF IN (X)HTML DOCUMENTS:

ONE PAGE FOR BOTH HUMANS AND MACHINES DON’T NEED TO REPEAT YOURSELF INTRODUCING NEW XHTML ATTRIBUTES

CURRENT WORK IS ONGOING ON RDFa 1.1: FOR PROFILES, ETC.

RDFa example

Triples are everywhere!

10/06/2013  

SUBJECT  

PREDICATE  OBJECT  

PREDICATE  OBJECT  OBJECT  …  

Defining semantics with ontologies

•  RDF PROVIDES A WAY TO WRITE ASSERTIONS ABOUT URIS

•  WHAT ABOUT THE SEMANTICS OF THESE ASSERTIONS, E.G. TO STATE THAT HTTP://XMLNS.COM/FOAF/0.1/KNOWS IDENTIFIES AN ACQUAINTANCE RELATIONSHIP?

•  ONTOLOGIES PROVIDE COMMON SEMANTICS FOR RESOURCES ON THE SEMANTIC WEB

Ontologies consist mainly of classes and properties – :Person a rdfs:Class .!– :father a rdfs:Property .!– :father rdfs:domain :Person .!– :father rdfs:range :Person .!

:Maciej

:Mark

:father

:Persona

:Persona

Notable ontologies

SOCIAL NETWORKS AND SOCIAL DATA:

FOAF, SIOC TAXONOMIES AND CONTROLLED VOCABULARIES:

SKOS, MOAT

Linked Data