General Introduction for Semantic Web and Linked Open Data

2012 INTERNATIONAL ASIAN SUMMER SCHOOL IN LINKED DATA
IASLOD 2012, August 13-17, 2012, KAIST, Daejeon, Korea

General Introduction
for Semantic Web and Linked Open Data

Hideaki Takeda
National Institute of Informatics
takeda＠nii.ac.jp
Hideaki Takeda / National Institute of Informatics

Semantic Web and Linked Data
• Semantic Web
– What is Semantic Web
– How to realize Semantic Web
• Metadata
• RDF
• RDFS
• OWL
• Linked Data
– What is Linked Data?
– The State-of-the-Art of Linked Data
• Linking Open Data (LOD)
– How to use Linked Data
• Linked Data Browser
• Linked Data Search Engine
• Linked Data Applications
– How to use RDF
• RDFa
– SPARQL

Semantic Web


The Aim of The Semantic Web
• "The Semantic Web is an extension of the current web in
which information is given well-defined meaning, better
enabling computers and people to work in cooperation."
The Semantic Web, Scientific American, May 2001, Tim Berners-Lee, James Hendler and Ora Lassila

• The Semantic Web is a vision: the idea of having data on
the web defined and linked in a way that it can be used by
machines not just for display purposes, but for
automation, integration and reuse of data across various
applications.
http://www.w3.org/2001/sw/


Semantic Web
• Realization of various information exchanging via Web

Automation
自動化
Integration
統合
Re-use of data
データの再利用


Next Generation Web?
• Evolution of Web
– HTML: Web for Display
– XML: Web with Syntax
– ?? : Web with Semantics

• Why should we embed semantics into Web?
From
– Web for Human
To
– Web for human and machines
cf. Web for machines


A brief introduction of XML
• Limitation of HTML
– Chaos by mixture of displaying and text structures
• e.g.,
– <h3></h3> should be used for “the third-level heading”, but are often
used just for bigger fonts
– <b></b> is specifying “bold” , not “emphasis”.
– Fixed Structure
• e.g.,
– If you need <h7></h7>….
– I need a structure just for my data
<h1> A list of lectures</h1>
<h2> Knowledge Sharing Systems</h2>
<h3> Lecturer： Hideaki Takeda</h3>
<h3>Wednesday 3rd</h3>


XML
• XML(eXtensible Markup Language)
– Can define original tags
– Represent logical structures of data
• DTD
– Do not include style information
<lecturelist>
• XST <lecture>
<title id=1234> Knowledge Sharing Systems</title>
<lecturer> Hideaki Takeda</lecturer>
<schedule>
<week>Wednesday</week>
<time>3rd</time>
</lecture>
...
</lecturelist>

Whey is XML not sufficient?
<person> <個人>
<name> Hideaki Takeda</name> <名前>Hideaki Takeda</名前>
<age> 20</age> <年齢> 20</年齢>
</person> </個人>

• What are specified by “person” and “name” ?
• Is “name” and “名前” the same?
• Is this description sufficient as a description for “person”?
• …

• In short, syntax alone cannot solve these problems

Architecture for the Semantic Web

Tim Berners-Lee http://www.w3.org/2002/Talks/09-lcs-sweb-tbl/

How to describe “meaning”?
• Need to describe “information on information”
– “Meaning of something” is a description (“meaning”)
to a description (“something”) in computers
– Metadata
• Data about data
• Need to architecture for common understanding
– Syntax (language or scheme)
– Vocabulary (ontology)


Metadata
• What is metadata?
– Data about data
– What one can say about any information object
• What is described as metadata?
– Content relates to what the object contains or is
about, and is intrinsic to an information object.
– Context indicates the who, what, why, where, how aspects
associated with the object's creation and is extrinsic to an
information object.
– Structure relates to the formal set of associations within or
among individual information objects and can be intrinsic
or extrinsic

Setting the State, Anne J.Gilliand-Swetland, Introduction to Metadata – Pathways to Digital
Information, Murthsa Baca (ed.), Getty Information Institute.

Metadata
• Metadata to individual information objects
– Bibliography，Dublin Core
• Metadata to part or structure of information objects
– Drawings，RDF，RDFS, OWL

Type：tractor
Owner：Taro
Product year：2002

Body

Axis:
Connect body to wheel

Wheel


A Layer model for Semantic Web
• RDF (Resource Description Framework)
– The most primitive model for metadata description
• SVO model
• Entity-Relation Model
• Semantic net
• RDF Schema
– Addition of “concept” to RDF
• class-subclass，constraints
• OWL
– More general concept description language
• Logical consistency
• Various class expressions
• Various constraints
• DAML-S
– Descriptions on processes


RDF (Resource Description
Framework)
• A framework to describe metadata
• Separation of model and syntax
• W3C Recommendation (2004)


RDF Model
• Element
– Resource:
• URI(Universal Resource Identifier)
• Literal(string)
– No need to be specified by Web
– Property:
• Attribute when describing resources
• URI or Literal just as Resource
– Statement: triad of resource, property, and
resource


RDF model
• Statement
– Creator of http://www-kasm.nii.ac.jp/~takeda is “Hideaki Takeda”
• Structure
– Resource (subject): http://www-kasm.nii.ac.jp/~takeda
– Property (predicate): Creator
– Value (object): “Hideaki Takeda”

Creator
http://www-kasm.nii.ac.jp/~takeda “Hideaki Takeda”

Resource Property Value


RDF model
• Creator of http://www-kasm.nii.ac.jp/~takeda is http://www.nii.ac.jp/staffid/123456 which
has name “Hideaki Takeda” and email “takeda@nii.ac.jp” ．

Creator
http://www-kasm.nii.ac.jp/~takeda http://www.nii.ac.jp/staffid/123456

name email

“Hideaki Takeda” “takeda@nii.ac.jp”


RDF model
• Creator of http://www-kasm.nii.ac.jp/~takeda has name
“Hideaki Takeda” email “takeda@nii.ac.jp” ．
Creator
http://www-kasm.nii.ac.jp/~takeda

name email

“Hideaki Takeda” “takeda@nii.ac.jp”


RDF syntax
• Creator of http://www-kasm.nii.ac.jp/~takeda is “Hideaki Takeda”

Creator
http://www-kasm.nii.ac.jp/~takeda “Hideaki Takeda”

Resource Property Value
<?xml version="1.0"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc="http://dublincore.org/2001/08/14/dces#">
<rdf:Description about="http://www-kasm.nii.ac.jp/~takeda">
<dc:Creator>Hideaki Takeda</dc:Creator>
</rdf:Description>
</rdf:RDF>
<rdf:RDF>
<rdf:Description about="http://www-kasm.nii.ac.jp/~takeda">
<dc:Creator rdf:resource=“Hideaki Takeda” />
</rdf:Description>
</rdf:RDF>

RDFS (RDF Schema)
• Stronger knowledge representation model
– RDF: ER model，semantic net
– RDF Schema: Frame model，object-oriented
paradigm
• Minimal definition
• Property-centered approach
• RDFS is defined as extension of RDF
• RDFS gives definitions of RDF descriptions


RDFS
• Class Definition
– rdfs:Resource
– rdfs:Class
– rdf:Property
– rdfs:ConstraintProperty
– rdfs:Literal
• Property Definition
– rdf:type
– rdfs:subClassOf
– rdfs:subPropertyOf
– rdfs:comment
– rdfs:label
– rdfs:seeAlso
– rdfs:isDefinedBy
• ConstraintProperty Definition
– rdfs:range RDFS Structure by RDF
– rdfs:domain Resource Description Framework(RDF) Schema Specification 1.0
http://www.w3.org/TR/2000/CR-rdf-schema-20000327/


RDF Schema
• rdfs:Class  Range
• rdfs:SubclassOf  Only one

– Detailed class  No cardinality

– Multiple  Domain
– Transivity  Multiple (or)
• rdf:type
– Indicate an instance of a
class
• rdf:property
– Attribute
• rdfs:subPropertyOf
– Detailed property
– Transivity

<rdf:RDF xml:lang="en" RDF Schema
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" “The class of person”
Animal

s
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
rdfs:comment
<rdfs:Class rdf:ID="Person">
Person
<rdfs:comment>The class of people.</rdfs:comment> d d
<rdfs:subClassOf rdf:resource="http://www.w3.org/ maritalStatus d
2000/03/example/ r ssn
classes#Animal"/> age
</rdfs:Class> MaritalStatus
r
<rdf:Property ID="maritalStatus"> rdfs:comment
<rdfs:range rdf:resource="#MaritalStatus"/> Integer
<rdfs:domain rdf:resource="#Person"/> t
t
</rdf:Property>
Married “Social Security Number”
<rdf:Property ID="ssn"> t Single
<rdfs:comment>Social Security Number</rdfs:comment> Windowed
<rdfs:range t = rdf:type
rdf:resource="http://www.w3.org/2000/03/example/classes#Integer"/> t d = rdfs:domain
<rdfs:domain rdf:resource="#Person"/> Divorced
r = rdfs:range
</rdf:Property> = class
<rdf:Property ID="age"> = class instance
<rdfs:range = property
rdf:resource="http://www.w3.org/2000/03/example/classes#Integer"/>
<rdfs:domain rdf:resource="#Person"/>
</rdf:Property>
<rdfs:Class rdf:ID="MaritalStatus"/>
<MaritalStatus rdf:ID="Married"/>
<MaritalStatus rdf:ID="Divorced"/>
Resource Description Framework(RDF) Schema Specification 1.0
<MaritalStatus rdf:ID="Single"/>
http://www.w3.org/TR/2000/CR-rdf-schema-20000327/
<MaritalStatus rdf:ID="Widowed"/>
</rdf:RDF> Hideaki Takeda / National Institute of Informatics

OWL(Web Ontology Language)
• More general knowledge representation
• Based on Description Logics
• Features
– Class
• Necessary condition / necessary and sufficient condition
• Class expression:
– Constraint by property
» Like slot definition of a class
» Type constraint (all/some), cardinality, typed cardinality
– Logical operation of classes: union, intersection, negation
– Property
• Multiple ranges and domains
• Specifying meta-property
– Import of definitions


Linked Data


Linked Data
• What is Linked Data?
• The State-of-the-Art of Linked Data
– Linking Open Data (LOD)
• How to use Linked Data
– Linked Data Browser
– Linked Data Search Engine
– Linked Data Applications
• How to use RDF
– RDFa
– SPARQL


Architecture for the Semantic Web
 The world of classes (Ontologies)
 The world of instances
(Linked Data)


Layers of Semantic Web
• Ontology
– Descriptions on classes
– RDFS, OWL
– Challenges for ontology building
• Ontology building is difficult by nature
– Consistency, comprehensiveness, logicality
• Alignment of ontologies is more difficult

Descriptions on classes
Ontology

インスタンスに関する記述
Linked Data


Layers of Semantic Web
• Linked Data
– Descriptions on instances (individuals)
– RDF + (RDFS, OWL)
– Pros for Linked Data
• Easy to write (mainly fact description)
• Easy to link (fact to fact link)
– Cons for Linked Data
• Difficult to describe complex structures
• Still need for class description (-> ontology)
Descriptions on classes
Ontology

Description on instances
Linked Data


Linked Data
 Linked Data is “Web of Data”
– Data published as RDF
– Can refer from outside
• The four rules for Linked Data


Linked Data
• The four rules for Linked Data
– Use URIs as names for things
• Give a URI to every object in the world!
– Use HTTP URIs so that people can look up those names.
• Don’t use URN
– When someone looks up a URI, provide useful information, using the
standards (RDF, SPARQL)
• Provide machine-readable data for URI
– Include links to other URIs. so that they can discover more things.
• Make data linked together just like Web

Linked Data, TBL, http://www.w3.org/DesignIssues/LinkedData.html


Linking Open Data (LOD)
• The project to collect published Linked Data
• Major Linked Data
• (Translated from the original resources)
– Dbpedia (Wikipedia) 270 Million Triples
– Geonames：Geo names and their latitudes and longitudes, 93 Million
Triples
– MusicBrainz：Music
– WordNet：Dictionary
– DBLP bibliography：Bibliography for technical papers. 28 Million Triples
– US Census Data: 1 Billion Triples
• （Crawling)
– FOAF (Friend Of A Friend)
• （Wrapper）
– Flickr Wrapper


LOD Cloud
(Linking Open Data)


http://dbpedia.org/page/Tokyo


http://en.wikipedia.org/wiki/Tokyo


How to use Linked Data

Linked Data Linked Data Linked Data
Browser Mashup Search Engine

Things Things Things Things Things


Linked Data Browser
• Browse linked data just as browsing web pages
– Show RDF data
– Prompt links to follow
• System/Service
– Mables
• Display data by following links
– Tabulator
• Firefox plugin/online
• Adding information in a single page
– Sig.ma
• Showing RDF resources which can be operated


Tabulator


Linked Data Search Engine
• Search RDF data with crawled data set
– Swoogle
– Sindice
– watson


http://sindice.com/


How to use Linked Data
• Semantic Data Mash-up Applications

– SemaPlorer
• http://btc.isweb.uni-koblenz.de/
– Dbpedia Mobile
• http://wiki.dbpedia.org/DBpediaMobile
– Bio2RDF
• http://bio2rdf.org/


DBpedia Mobile


Bio2RDF
• Search LOD in
bioscience
• Translate data into RDF
if not


Bio2RDF


RDFa
• Add extra structured content to the (X)HTML
pages
– adds new (X)HTML/XML attributes
• “RDF in attributes”
– Programs can extract those and turn into RDF
– Flexibility for using Literals and URI resources


Principles of RDFa
• RDF contents are defined through XML
attributes (no elements)
• XML/HTML tree structure is used
• Various attributes are defined by RDFa
– Some attributes (@href, @rel) are also reused
• The text content can be also reused


Examples
http://example.com/alice/posts/trouble_with_bob
<div xmlns:dc="http://purl.org/dc/elements/1.1/">
<h2 property="dc:title">The trouble with Bob</h2>
<h3 property="dc:creator">Alice</h3>
...
</div>

In N3
<http://www.example.com/alice/posts/trouble_with_bob>
<http://purl.org/dc/elements/1.1/title> "The Trouble with Bob";
<http://purl.org/dc/elements/1.1/creator> "Alice" .


<div xmlns:dc="http://purl.org/dc/elements/1.1/">
<div about="/alice/posts/trouble_with_bob">
<h3 property="dc:creator">Alice</h3>
...
</div>
<div about="/alice/posts/jos_barbecue">
<h2 property="dc:title">Jo's Barbecue</h2>
<h3 property="dc:creator">Eve</h3>
...
</div>
...
</div>


<div about="/alice/posts/trouble_with_bob">
The trouble with Bob is that he takes much better photos than I do:
<div about="http://example.com/bob/photos/sunset.jpg">
<img src="http://example.com/bob/photos/sunset.jpg" />
<span property="dc:title">Beautiful Sunset</span>
by
<span property="dc:creator">Bob</span>.
</div>
</div>


<div typeof="foaf:Person" xmlns:foaf="http://xmlns.com/foaf/0.1/">
<p property="foaf:name"> Alice Birpemswick </p>
<p> Email: <a rel="foaf:mbox" href="mailto:alice@example.com">alice@example.com</a></p>
<p> Phone: <a rel="foaf:phone" href="tel:+1-617-555-7332">+1 617.555.7332</a> </p>
</div>


Using RDFa
• RDF Validator
– http://validator.w3.org/
• RDF Distiller
– http://www.w3.org/2007/08/pyRdfa/


<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN"
"http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:foaf="http://xmlns.com/foaf/0.1/" <body about="http://example.org/john-d/#me">
xmlns:dc="http://purl.org/dc/elements/1.1/" <h1>John's Home Page</h1>
version="XHTML+RDFa 1.0" xml:lang="en"> <p>My name is <span property="foaf:nick">John D</span>
<head> and I like
<title>John's Home Page</title> <a href="http://www.neubauten.org/" rel="foaf:interest"
<base href="http://example.org/john-d/" /> xml:lang="de">Einsturzende Neubauten</a>.
<meta property="dc:creator" content="Jonathan Doe" /> </p>
<link rel="foaf:primaryTopic" <p>
href="http://example.org/john-d/#me" /> My <span rel="foaf:interest"
</head> resource="urn:ISBN:0752820907">favorite
book is the inspiring <span about="urn:ISBN:0752820907">
<cite property="dc:title">Weaving the Web</cite> by
<span property="dc:creator">Tim Berners-Lee</span></span>
</span>
</p>
</body>
</html>

<http://example.org/john-d/> <http://xmlns.com/foaf/0.1/primaryTopic> <http://example.org/john-
d/#me>.
<http://example.org/john-d/> <http://purl.org/dc/elements/1.1/creator> "Jonathan Doe"@en.
<http://example.org/john-d/#me> <http://xmlns.com/foaf/0.1/nick> "John D"@en.
<http://example.org/john-d/#me> <http://xmlns.com/foaf/0.1/interest> <http://www.neubauten.org/>.
<http://example.org/john-d/#me> <http://xmlns.com/foaf/0.1/interest> <urn:ISBN:0752820907>.
<urn:ISBN:0752820907> <http://purl.org/dc/elements/1.1/title> "Weaving the Web"@en.
<urn:ISBN:0752820907> <http://purl.org/dc/elements/1.1/creator> "Tim Berners-Lee"@en.

Summary
• Linked Data is the practical application of
Semantic Web
– The bottom-up approach
– Postpone the ontology issue
• A technological solution for data sharing
– Data science
– Open Government


General Introduction for Semantic Web and Linked Open Data

Recommended

Recommended

More Related Content

What's hot

What's hot (9)

Similar to General Introduction for Semantic Web and Linked Open Data

Similar to General Introduction for Semantic Web and Linked Open Data (20)

More from National Institute of Informatics (NII)

More from National Institute of Informatics (NII) (20)

Recently uploaded

Recently uploaded (20)

General Introduction for Semantic Web and Linked Open Data