General Introduction for Semantic Web and Linked Open Data

Hideaki Takeda / National Institute of Informatics

General Introduction for Semantic Web and Linked Open Data

Hideaki TakedaNational Institute of Informatics

takeda＠ nii.ac.jp

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


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/

http://www.scientificamerican.com/2001/0501issue/0501berners-lee.html

http://www.scientificamerican.com/2001/0501issue/0501berners-lee.html


Semantic Web• Realization of various information exchanging via Web

自動化統合

データの再利用

AutomationIntegration

Re-use of data


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 machinescf. 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

• XST <lecturelist><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?

• 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

<person> <name> Hideaki Takeda</name> <age> 20</age></person>

< 個人 > < 名前 >Hideaki Takeda</ 名前 > < 年齢 > 20</ 年齢 ></ 個人 >


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 ： tractorOwner ： Taro

Product year ：2002

Axis:Connect body to wheel

Wheel

Body


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”

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

Resource Property Value

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



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 “[email protected]” ．


“Hideaki Takeda”

Creatorhttp://www.nii.ac.jp/staffid/123456

“[email protected]”

name email


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

email “[email protected]” ．


“Hideaki Takeda”

Creator

“[email protected]”

name email


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

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

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:domain

Resource Description Framework(RDF) Schema Specification 1.0http://www.w3.org/TR/2000/CR-rdf-schema-20000327/

RDFS Structure by RDF


RDF Schema• rdfs:Class• rdfs:SubclassOf

– Detailed class– Multiple– Transivity

• rdf:type– Indicate an instance of a

class• rdf:property

– Attribute• rdfs:subPropertyOf

– Detailed property– Transivity

Range Only one

No cardinality Domain

Multiple (or)


RDF Schema<rdf:RDF xml:lang="en" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"><rdfs:Class rdf:ID="Person"> <rdfs:comment>The class of people.</rdfs:comment> <rdfs:subClassOf rdf:resource="http://www.w3.org/　　　 2000/03/example/　 classes#Animal"/></rdfs:Class><rdf:Property ID="maritalStatus"> <rdfs:range rdf:resource="#MaritalStatus"/> <rdfs:domain rdf:resource="#Person"/></rdf:Property><rdf:Property ID="ssn"> <rdfs:comment>Social Security Number</rdfs:comment> <rdfs:range

rdf:resource="http://www.w3.org/2000/03/example/classes#Integer"/> <rdfs:domain rdf:resource="#Person"/></rdf:Property><rdf:Property ID="age"> <rdfs:range

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"/><MaritalStatus rdf:ID="Single"/><MaritalStatus rdf:ID="Widowed"/></rdf:RDF>

Animal

Person

ssnage

maritalStatus

s

d

MaritalStatus

r

“The class of person”

rdfs:comment

Integer

d

r

d

“Social Security Number”

rdfs:comment

t = rdf:typed = rdfs:domainr = rdfs:range = class = class instance = property

Resource Description Framework(RDF) Schema Specification 1.0http://www.w3.org/TR/2000/CR-rdf-schema-20000327/

Married

Divorced

Single

Windowed

t

t

t

t


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


Linked Data






Architecture for the Semantic Web


The world of instances (Linked Data)

The world of classes (Ontologies)


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

インスタンスに関する記述

Ontology

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

Description on instances

Ontology

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

http://www.w3.org/DesignIssues/LinkedData.html


Linked Data






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


http://www4.wiwiss.fu-berlin.de/bizer/pub/lod-datasets_2008-09-18.html



LOD Cloud(Linking Open Data)


http://dbpedia.org/page/Tokyo

http://dbpedia.org/page/Tokyo


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

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




Linked Data






How to use Linked Data

Things Things Things Things Things

Linked Data Browser

Linked Data Mashup

Linked Data Search Engine


Linked Data






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






Linked Data Search Engine

• Search RDF data with crawled data set– Swoogle– Sindice– watson


http://sindice.com/

http://sindice.com/



Linked Data






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/

http://btc.isweb.uni-koblenz.de/

http://wiki.dbpedia.org/DBpediaMobile


DBpedia Mobile


Bio2RDF• Search LOD in

bioscience• Translate data into RDF

if not


Bio2RDF


Linked Data






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• Varios attributes are defined by RDFa

– Some attributes (@href, @rel) are also reused• The text content can be also reused


Examples<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>

http://example.com/alice/posts/trouble_with_bob

<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" .

In N3


<div xmlns:dc="http://purl.org/dc/elements/1.1/"> <div about="/alice/posts/trouble_with_bob"> <h2 property="dc:title">The trouble with Bob</h2> <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"> <h2 property="dc:title">The trouble with Bob</h2> 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:[email protected]">[email protected]</a></p> <p> Phone: <a rel="foaf:phone" href="tel:+1-617-555-7332">+1 617.555.7332</a> </p> </div>


<div xmlns:foaf="http://xmlns.com/foaf/0.1/" about="#me" rel="foaf:knows"> <ul> <li typeof="foaf:Person"> <a property="foaf:name" rel="foaf:homepage" href="http://example.com/bob">Bob</a> </li> <li typeof="foaf:Person"> <a property="foaf:name" rel="foaf:homepage" href="http://example.com/eve">Eve</a> </li> <li typeof="foaf:Person"> <a property="foaf:name" rel="foaf:homepage" href="http://example.com/manu">Manu</a> </li> </ul> </div>


Using RDFa

• RDF Validator– http://validator.w3.org/

• RDF Distiller– http://www.w3.org/2007/08/pyRdfa/

http://validator.w3.org/

http://validator.w3.org/

http://www.w3.org/2007/08/pyRdfa/


<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.

<?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/" xmlns:dc="http://purl.org/dc/elements/1.1/" version="XHTML+RDFa 1.0" xml:lang="en"> <head> <title>John's Home Page</title> <base href="http://example.org/john-d/" /> <meta property="dc:creator" content="Jonathan Doe" /> <link rel="foaf:primaryTopic" href="http://example.org/john-d/#me" /> </head>

<body about="http://example.org/john-d/#me"> <h1>John's Home Page</h1> <p>My name is <span property="foaf:nick">John D</span> and I like <a href="http://www.neubauten.org/" rel="foaf:interest" xml:lang="de">Einsturzende Neubauten</a>. </p> <p> My <span rel="foaf:interest" 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>


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

Documents

semantic webthe semantic

web automationintegrationre

current web

problems hideaki takeda

reuse of data

semantic webhow

linked datasemantic

description sufficient