linked data tutorial

Bernhard Haslhofer, Linked Data Tutorial

Linked Data Tutorial

@ Vlaams Theater Instituut

Brussels, 03/2009

[email protected]

Friday, March 6, 2009

mailto:[email protected]



Contents

• Motivation for Linked Open Data (LOD)

• Base Technologies

• The Linked Data Principles

• Publishing Solutions and Tools

• Vocabularies & Interoperability Issues

• Demos + Discussion

2


Bernhard Haslhofer, Linked Data Tutorial 3

How do we look up information about things?



... about this book?



... about this play?



... about these concepts?



... about things?

...that book? ...this play? ...these concepts?

we look up their names

and see what we can find out

Metamorphosis Effi Briest Love / Hate



An Example



The Hallstatt culture



formerly

Controlled Vocabulary

10



formerly

Metadata

Identifier

11



then

Controlled Vocabulary

Metadata

Identifier

12



now

13



If information is not available on the Web, people tend to ignore it.

14



Current Situation

15

Database

Web Server

JDBC HTML

Web



The current Web is a Web of Documents intended for human interpretation.

16



The data are still locked in closed silos.

17

Database

Database

Database

Database Database

Database



Other applications can not access and process these data unless...

18



Existing Approaches

19

OAI-PMH

Web ServicesSOAP

WSDL

UDDI

REST

Atom

RMI CORBA

RPC

DCOM

OAI-ORE

Z39.50

RSS

JSON

SRU/SRQ

FTPCD-ROM

CD-ROM



The linked data vision is to...

20



Database

Documents

Data



• open the data silos and get rid of repository-centric mindset

• publish data of public interest on the Web

• in a way that other applications can access and interpret the data

• using common Web technologies

22



make it possible for applications to look up (meta)data ...

23



... about things

...that book? ...this play? ...these concepts?

by looking up their names

on the Web

http://dbpedia.org/resource/The_Metamorphosis

http://dbpedia.org/resource/Effi_Briest

http://dbpedia.org/resource/Love

http://dbpedia.org/resource/Hatred






http://dbpedia.org/page/Effi_Briest





http://dbpedia.org/page/Love









To do so, we need some technology

25



• Names (Identifiers) for resources in an open environment

• dereferencable URI = HTTP URI (URL)

26

Uniform Resource Identifier (URI)

http://dbpedia.org/resource/Hallstatt_culture


http://dbpedia.org/page/Hallstatt_culture





• a model for representing metadata on the Web

• in the form of statements (triples)

27

Resource Description Framework (RDF)


“The Hallstatt culture was ...”

“Hallstatt culture”skos:subject

dbpprop: abstract

rdfs: label

http://dbpedia.org/resource/

Category:Iron_Age_Europe






http://thesaurus.com/concept/IronAge







• for exchanging RDF data

• serialization & de-serialization

28

RDF/XML, N3, Turtle, etc.

<rdf:Description rdf:about=” http://dbpedia.org/resource/Hallstatt_culture”>

<dbpprop:abstract>The Hallstatt culture was...</dbpprop:abstract>

<skos:subject rdf:resource=”http://dbpedia.org/resource/

Category:Iron_Age_Europe”>

<rdfs:label>Hallstatt culture</rdfs:label>

</rdf:Description>









• languages for describing vocabularies

29

RDFS & OWL

rdf: type

dbpprop: abstract skos: subject rdfs: label

rdf: typerdf: type

rdf: Property











• a language for describing controlled vocabularies

30

Simple Knowledge Organization System (SKOS)

dbpedia:Category: Iron_Age_Europe

“Iron Age Europe”

skos:prefLabel

xyz: HallstattCultureskos:narrower

“Hallstatt Period” “Hallstatt Culture”

skos:prefLabel

xyz: LateneCulture

skos:altLabel“La Tène Period”

skos:prefLabel

skos:narrower











• a query language & protocol for accessing RDF data via the Web

31

SPARQL

SELECT ?uri

WHERE {

?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe>.

}





The vision is becoming reality...

32



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

<http://dbpedia.org/resource/Hallstatt_culture >

p:abstract “Die Hallstattzeit bezeichnet...” @de

p:abstract “The Hallstatt culture was...” @en

rdfs:label “Hallstatt culture”@en;

rdfs:label “Hallstattzeit” @de;

rdfs:label “Civilisation de Hallstatt” @fr;

rdfs:label “ハルシュタット文明” @jp;

skos:subject dbpedia:Category:Iron_Age_Europe;

...




http://dbpedia.org/resource/Iron_Age




...

p:hasPhotoCollection <http://www4.wiwiss.fu-berlin.de/flickrwrappr/

photos/Hallstatt_culture>;

...




http://www4.wiwiss.fu-berlin.de/flickrwrappr/photos/Hallstatt_culture





Library of Congress Subject Headings

35



The LOD idea in brief

• expose data on the Web, not just documents

• interlink these data with those of other data sources

37



LOD benefits

• other humans and applications can

• easily access your data using Web technologies

• follow the links in order to obtain further contextual information

• links to your data and search engine indices can increase the visibility of your data

38


“Stop hugging your data”

Sir Tim Berners-Lee, 2009

(c) Paul Miller, http://www.slideshare.net/cloudofdata/toward-the-data-cloud


http://www.flickr.com/photos/_-amy-_/3167333250/





Contents







40



The Semantic Web Layer Cake

41

URI Unicode

XML

Data Interchange: RDF

RDF-S

Rules:

RIF

Ontology:

OWLQuery:

SPARQL

Unifying Logic

Proof

Crypto

Trust

User Interface & Applications

Vocabulary:

SKOS



From a Database point of view

42

Database Domain Semantic Web

Relational Model(Tables)

URI, RDF

SQL DDL(Create Table table-name ...)

RDFS, OWL

SQL Query Language(Select * from ...)

SPARQL



Uniform Resource Identifiers (URI)

• Unambiguous name for “something”

• for a digital resource

• for a concept within a vocabulary

• etc..

• “A URI is a compact sequence of characters that identifies an abstract or physical resource”[RFC 3986]

43


http://dbpedia.org/resource/Hallstatt












• “Uniform”:

• different types of resource identifiers in the same context

• common syntactic conventions

• “Resource”:

• whatever might be identified by a URI

• “Identifier”:

• distinguish one resource from other ones

44




• An URI can be classified as locator (URL), name (URN), or both

• Uniform Resource Locator (URL)

• a means for locating the resource by describing its primary access mechanism (e.g., http://example.com)

• Uniform Resource Name (URN)

• a means for naming the resource (e.g., urn:example.com:animal)

45




• Generic syntax - a hierarchical sequence of components

46

foo://example.com:8042/over/there?name=ferret#nose \_/ \________________/\_________/ \_________/ \__/ | | | | | scheme authority path query fragment | ______________________|_ / \ / \ urn:example:animal:ferret:nose

URI = scheme “:” hier-path [ “?” query ] [ “#” fragment ]




• Example URIs:

47

ftp://ftp.is.co.za/rfc/rfc1808.txt

http://www.ietf.org/rfc/rfc2396.txt

ldap://[2001:db8::7]/c=GB?objectClass?one


news:comp.infosystems.www.servers.unix

tel:+1-816-555-1212

urn:oasis:names:specification:docbook:dtd:xml:4.1.2






http://www.servers.unix

http://www.servers.unix


Internationalized Resource Identifiers (IRI)

• can we use non-ASCII characters in URIs (e.g., Umlaut, Chinese, Arabic, Hebrew, etc...)?

• extend the syntax of URI so that a much wider repertoire of characters can be used

• uses Universal Character Set (ISO 10646)

• mapping from IRIs to URIs

• IRIs can be used wherever URIs are allowed

48




49

URI Unicode

XML


RDF-S

Rules:

RIF

Ontology:

OWLQuery:

SPARQL

Unifying Logic

Proof

Crypto

Trust


Vocabulary:

SKOS




• The basic structural element of RDF is the statement

50

http://dbpedia.org/resource/Hallstatt_culture “Hallstatt culture”

skos:subject

rdfs: label

http://dbpedia.org/resource/Category:Iron_Age_Europe

Subject Predicate Object

Subject Property Value












• The subject of a statement is always a (URI) resource

• The predicate of a statement is always a (URI) resource

• The object of a statement can be a resource (URI) or a typed literal

• An RDF statement forms a triple

• Triples can be merged into a set of triples, forming a directed labeled graph

51




• Literals can be plain or typed using arbitrary datatypes

• It is recommended to use XML Schema datatypes [XMLS2]

52

http://dbpedia.org/resource/Hallstatt “Hallstatt”

geo:long

rdfs: label

“13.646667”^^<http://www.w3.org/2001/XMLSchema#float>






http://www.w3.org/2001/XMLSchema#








• Support for multilingual labels

• Plain literals may have a language tag, as defined by RFC 3066

53

http://dbpedia.org/resource/Hallstatt “Hallstatt”@de

rdfs:label

rdfs: label

“ハルシュタット (オーバーエスターライヒ州)”@jp

“Гальштат”@ru

rdfs: label








• Blank nodes can be used to model structured information that needs no URI by itself

• they must still be distinguishable within an RDF graph. This is done using blank node identifiers

54

http://www.ex.com/

staff#85740

"Bedford"

http://www.ex.com/#city

http://www.ex.com/#address

"1501 Grant

Avenue""Massachusetts"

"01730"http://www.ex.com/#street http://www.ex.com/#state

http://www.ex.com/#zipcode




• Containers allow to describe groups of things

• Bag (unordered set), Seq (ordered set), Alt (choice)

55

http://www.ex.com/

courses#6.001

http://www.ex.com/students#students

http://www.w3.org/1999/02/22-rdf-

syntax-ns#Bag

http://www.ex.com/students#Amy

http://www.ex.com/

students#Mohamed

http://www.ex.com/students#Johann

http://www.ex.com/students#Maria

http://www.w3.org/1999/02/22-rdf-syntax-ns#type

http://www.w3.org/1999/02/22-rdf-syntax-ns#_1




blank node




• Collections allow the definition of closed containers

• define the exact set of items in a collection

56

http://www.ex.com/

courses#6.001

http://www.ex.com/students#students

http://www.ex.com/students#Amy

http://www.ex.com/

students#Mohamed

http://www.ex.com/students#Johann

http://www.w3.org/1999/02/22-rdf-

syntax-ns#nil

http://www.w3.org/1999/02/22-rdf-syntax-ns#first

http://www.w3.org/1999/02/22-rdf-syntax-ns#rest








• RDF can be serialized using various syntax formats:

57

<?xml version=”1.0”?>

<rdf:RDF xmlns:rdf=”http://www.w3.org/1999/02/22-rdf-syntax-ns#” xmlns:rdfs=”http://

www.w3.org/2000/01/rdf-schema#” xmlns:dbpprop=”http://dbpedia.org/property/” .... >

<rdf:Description rdf:about=” http://dbpedia.org/resource/Hallstatt_culture”>

<dbpprop:abstract>The Hallstatt culture was...</dbpprop:abstract>

<skos:subject rdf:resource=” http://dbpedia.org/resource/

Category:Iron_Age_Europe”>

<rdfs:label>Hallstatt culture</rdfs:label>

</rdf:Description>RDF/XML


http://www.w3.org/1999/02/22-rdf-syntax-ns#


http://dbpedia.org/about/html/http://www.w3.org/2000/01/rdf-schema#












• RDF can be serialized using various syntax formats:

58

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>

@prefix rdfs: <http://dbpedia.org/about/html/http://www.w3.org/2000/01/rdf-schema#>

@prefix dbpprop: <http://dbpedia.org/property/>

<http://dbpedia.org/resource/Hallstatt_culture>

dbpprop:abstract “The Hallstatt culture was...” ;

skos:subject < http://dbpedia.org/resource/Category:Iron_Age_Europe > ;

rdfs:label “Hallstatt culture” . Turtle / N3












• Reification

• allows to describe other statements; i.e. make statements about other statements

• rarely used in practice

59




60

URI Unicode

XML


RDF-S

Rules:

RIF

Ontology:

OWLQuery:

SPARQL

Unifying Logic

Proof

Crypto

Trust


Vocabulary:

SKOS



RDF Schema (RDFS)

• extends RDF with the possibility to define classes and associated properties

• allows RDF applications to agree on a common data description vocabulary

• is implemented on top of RDF - each valid RDFS document is a valid RDF document

61



RDF Schema (RDFS)

• classes and subclass relationships

62

rdfs: Class

rdfs: subClassOf

yago: CitiesAndTownsInUpperAustria


rdf:type

rdf:type

yago: City

rdf:type









RDF Schema (RDFS)

• properties and subPropertyOf relationships

63

rdf: Property

rdfs: subPropertyOfdbProp: abstractdcterms: description

rdf:type rdf:type

Note: in reality, dbpedia: abstract is no subject of dcterms; description





RDF Schema (RDFS)

• domain and range relationships

64

xyz: Article

xsd: string

dbProp: abstract

rdfs: domain

rdfs: range

rdfs: Class

rdf: type







RDF Schema (RDFS)

• comments: rdfs: comment

• human-readable names for resources: rdfs: label

• machine-readable information: rdfs: seeAlso, rdfs: isDefinedBy

65



RDF Schema (RDFS)

• Shortcomings:

• no cardinality constraints on properties

• no inverse / transitive / symmetric properties

• no union / disjoint / enumeration classes

66




67

URI Unicode

XML


RDF-S

Rules:

RIF

Ontology:

OWLQuery:

SPARQL

Unifying Logic

Proof

Crypto

Trust


Vocabulary:

SKOS



Web Ontology Language (OWL)

• An extension of RDFS

• logic based; provides automated reasoning support

• Three “sub-languages”

• OWL Full: maximum expressiveness and syntactic freedom

• OWL DL: restricted to first order logic; decidable

• OWL Lite: easy to implement; provides mechanisms for creating classification hierarchies with simple constraints

68




• owl:Class defines a group of individuals that belong together because of shared properties

• owl:Thing is the class of all individuals, and a superclass of all OWL classes

69

dbpedia-owl: Place http://dbpedia.org/resource/Hallstatt

rdf:type

rdf:type

owl: Class

rdfs: Class

owl: Thing

rdfs: subClassOf

rdfs: subClassOf
















• DatatypeProperty: properties whose value is a literal

• ObjectProperty: properties whose value is an individual

70

rdf:type

dbPedia-owl: id

dbPedia-owl: region

dbPedia-owl: WorldHeritageSite

xsd: string

dbpedia-owl: PopulatedPlace

owl: DatatypeProperty

owl: ObjectProperty

rdf: Property

rdf:type

rdfs: subClassOf

rdfs: range

rdfs: range

rdfs: domain

rdfs: domainrdfs: subClassOf






























• owl: equivalentClass states that two classes are equivalent, i.e., they have the same instances

71

dbpedia: Car dbpedia: Automobileowl: equivalentClass

Note: DBpedia actually uses dbpedia: redirect








• owl: equivalentProperty states that two properties are equivalent; they relate one individual to the same set of other individuals

72

myOnt: abstract dbpprop: abstractowl: equivalentProperty








• owl:sameAs states that two individuals are the same

73

fbase: Hallstatt cultureowl: sameAshttp://dbpedia.org/resource/

Hallstatt_culture










• owl: inverseOf (e.g., hasChild inverseOf hasParent)

• owl: transitiveProperty (e.g., hasAncestor)

• owl: symmetricProperty (e.g., knows)

• owl: functionalProperty (e.g. hasPrimaryEmployer)

• owl: inverseFunctionalProperty (e.g., hasSocialSecurityNumber)

74




• owl: allValuesFrom restricts properties to values of classes

• owl: minCardinality restricts a property’s minimum cardinality with respect to a class

• owl: maxCardinalty restricts a property’s maximum cardinality with respect to a class

• owl: cardinality = shortcut for min/maxCardinality

75




• owl: intersectionOf (e.g., EmployedPerson = Person ∩ CorporateResources)

• owl: unionOf (e.g., NorthAmericanCitizen = USCitizen ∪ CanadaCitizen)

• owl: complementOf (e.g., JuniorResearcher = Researcher - SeniorResearcher)

• owl: disjointWith (e.g., Woman ∩ Man = ∅)

76




77

URI Unicode

XML


RDF-S

Rules:

RIF

Ontology:

OWLQuery:

SPARQL

Unifying Logic

Proof

Crypto

Trust


Vocabulary:

SKOS




• a family of formal languages for the definition and representation of controlled vocabularies on the Web

• thesauri

• classification schemes

• taxonomies

• subject-heading systems

• an application of RDF/S & OWL

78




• vocabulary terms are represented as concepts identified by URIs

79

dbpedia: Category: Iron_Age_Europe

skos: Concept

rdf: type

xyz: HallstattCulture

rdf: type












• concepts have preferred, alternate & hidden labels

• label is either preferred or alternate or hidden; one per language

80

xyz: HallstattCulture

“Hallstatt Period@en”

“Hallstatt Kultur@de”skos:prefLabel

skos: prefLabel

“Hallstatt Culture@en”

skos:altLabel






• concepts can be organized in hierarchies by (the inverse) skos: broader or skos: narrower relationships

81

dbpedia: Category: Iron_Age_Europe

xyz: HallstattCultureskos: narrower

dbpedia: Category: Iron_Age dbpedia: Category: Prehistoric_Europe

skos: broader skos: broader

Note: in DBPedia this narrower rel. does not exist
















• concepts can be associated by non-hierarchical (non-transitive) skos:related properties

82

xyz: HallstattCulture xyz: HallstattCivilizationskos: related






• concepts can have notes for general documentation purposes

• scopeNote: an indication how the use of a concept is limited in indexing practice

• definition: an explanation of the intended meaning

• example: supplies an example of the use of a concept

• historyNote: describes significant changes to the meaning of a concept

83




• concepts can be defined as part of well-defined concept schemes (thesauri, classification schemes)

84

xyz: HallstattCulture xyz: HallstattCivilization

skos: inScheme

ex: archeologyThesaurus

skos: inScheme

“Archeology Thesaurus”

“John Doe”

dc:title

dc:creator








• Other features

• SKOS allows the mapping between different concept schemes

• concepts can be organized in collections

• relationships between concept labels

• definition of broaderTransitive and narrowerTransitive relationships

• ....

85




86

URI Unicode

XML


RDF-S

Rules:

RIF

Ontology:

OWLQuery:

SPARQL

Unifying Logic

Proof

Crypto

Trust


Vocabulary:

SKOS



SPARQL

• is a query language that allows to access RDF data

• currently read-only; no update or delete

• based on matching graph patterns

• is a protocol that defines how queries and results can be transported over a network (over the Web)

87



SPARQL

• a simple query example

88

SELECT ?uri

WHERE {


}

uri...

dbpedia: Hallstatt_culture

...







SPARQL

• querying multiple variables

89

SELECT ?uri ?abstract

WHERE {


?uri dbpprop:abstract ?abstract .

}

uri abstract...

dbpedia: Hallstatt_culture The Hallstatt culture was the...

dbpedia: Hallstatt_culture Гальшта́тская культу́ра ...









SPARQL

• querying and filtering literal values

90

SELECT ?uri ?label

WHERE {

?uri rdfs:label ?label .

?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe> .

FILTER regex(?label, “culture”, “i”)

}uri label

dbpedia: Basarabi_culture Basarabi Culture

... ...

dbpedia: Hallstatt_culture Hallstatt Culture







SPARQL

• optional graph patterns

91

SELECT ?uri ?label ?image

WHERE {



OPTIONAL { ?uri foaf:img ?image }.

}





SPARQL

• optional graph patterns with constraints

92

SELECT ?uri ?label ?image

WHERE {



OPTIONAL {

?uri foaf:img ?image .

FILTER regex(?image, “jpg”, “i”) .

} .

}





SPARQL

• matching alternatives

93

SELECT ?uri ?classification

WHERE {


{ ?uri rdf:type ?classification . }

UNION

{ ?uri skos:subject ?classification . }

}





SPARQL

• solution modifiers

94

SELECT ?uri ?name

WHERE {


?uri rdfs:label ?name

}

ORDER BY ?name

LIMIT 10

OFFSET 5





SPARQL

• Other SPARQL features:

• rich set of FILTER expressions (see xquery functions)

• CONSTRUCT, DESCRIBE, ASK queries

• Named Graphs

95




96

URI Unicode

XML


RDF-S

Rules:

RIF

Ontology:

OWLQuery:

SPARQL

Unifying Logic

Proof

Crypto

Trust


Vocabulary:

SKOS



References

• General

• T. Berners-Lee, J. Hendler, O. Lassila: The Semantic Web. Scientific American, May 2001.

• URI

• T. Berners-Lee, R. Fielding, L. Masinter: Uniform Resource Identifier (URI): Generic Syntax (RFC 3986), January 2005.

• M. Duerst, M. Suignard: Internationalized Resource Identifiers (IRIs) (RFC 3987), January 2005.

• RDF/S

• F. Manola, E. Miller: RDF Primer. W3C Recommendation, February 2004.

• D. Brickley, R.V. Guha: RDF Vocabulary Description Language 1.0: RDF Schema. W3C Recommendation, February 2004.

97



References• OWL

• Deborah L. McGuiness, Frank van Harmelen (eds.): OWL Web Ontology Language Overview. W3C Recommendation 10 February 2004. Available at http://www.w3.org/TR/owl-features/

• Nataly F. Noy, Deborah L. McGuinness: Ontology Development 101: A Guide to Creating Your First Ontology. Available at http://www-ksl.stanford.edu/people/dlm/papers/ontology-tutorial-noy-mcguinness.pdf

• SKOS

• SKOS Primer: http://www.w3.org/TR/2008/WD-skos-primer-20080829/

• SPARQL

• Eric Prud’hommeaux, Andy Seaborne (eds.): SPARQL Query Language for RDF. W3C Candidate Recommendation 14 June 2007, available at http://www.w3.org/TR/rdf-sparql-query

98


http://www.w3.org/TR/owl-features/

http://www.w3.org/TR/owl-features/

http://www-ksl.stanford.edu/people/dlm/




http://www.w3.org/TR/2008/WD-skos-primer-20080829/

http://www.w3.org/TR/2008/WD-skos-primer-20080829/


Contents







99



The 4 principles

• Use URIs as names for things

• Use HTTP URIs so that people can look up those names

• When someone looks up a URI, provide useful information

• Include links to other other URIs, so that they can discover more things

100



Use HTTP URIs....

101



http://dbpedia.org/resource/Category:World_Heritage_Sites_in_Austria















Provide useful information ... for humans

102



Provide useful information ... for machines

103


p:abstract “Die Hallstattzeit bezeichnet...” @de

p:abstract “The Hallstatt culture was...” @en

rdfs:label “Hallstatt culture”@en;

rdfs:label “Hallstattzeit” @de;

rdfs:label “Civilisation de Hallstatt” @fr;

rdfs:label “ハルシュタット文明” @jp;

skos:subject dbpedia:Category:Iron_Age_Europe;

...





Provide useful information for humans and machines

104

• return different HTTP responses depending on HTTP-Accept-Header



Provide useful information for humans and machines

105

• best practice: also assign names (URIs) to various representations


http://dbpedia.org/data/Hallstatt_culture.rdf


Accept: text/htmlAccept: application/rdf+xml


http://db

http://db

http://db

http://db

http://db

http://db

http://db

http://db

http://db

http://db

http://db

http://db

http://db

http://db


Include links

106

http://rdf.freebase.com/ns/guid.9202a8c04000641f8000000000239c44

owl: sameAs



dbpprop: hasPhotoCollection















Include links

• other common properties

• rdfs: seeAlso

• foaf: knows

• foaf: based_near

• foaf: topic_interest

107



Include links

• manual link generation

• only for small data sets

• automatic link generation

• pattern-based algorithms (e.g., same ISBN number)

• more complex property-based algorithms

• see record-linkage problem in database domain

108



Benefit

• Clients can easily look up names and retrieve information and follow the links

109



References

• Berners-Lee 2006: Linked Data. Available at http://www.w3.org/DesignIssues/LinkedData.html

• Bizer et al.: How to Publish Linked Data on the Web. Available at: http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/

110


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




http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/





Contents







111



Relational Databases

112

Triplify D2R Server Virtuoso RDF Views

Technology

SPARQL Endpoint

Mapping Language

Mapping Generation

Scalability

Scripting languages (PHP) Java Middleware Solution

- Yes Yes

SQL RDF based RDF based

Manual Semi-automatic Manual

Medium-high(but no SPARQL) medium high

(c) Sören Auer, http://www.slideshare.net/soeren1611/linked-data-tutorial-presentation-955375


http://www.slideshare.net/soeren1611/linked-data-tutorial-presentation-955375





Triplify

• Goal: expose semantics available in RDBMS as simple as possible

• Available for most popular Web app languages

• PHP (ready), Ruby/Python (under dev.)

• Works with most popular Web app databases

• MySQL, PHP-PDO DBs (SQLite, Oracle, DB2, MS SQL, PostgreSQL)

113



Triplify

• Configuration

• number of SQL queries selecting information, which should be made publicly available

114

SELECT id, name AS ‘foaf:name’ FROM users



Triplify

115

!""#$%&'()'*()+,-).&'*)/0&12(3')4.#"'5)6%'*)&)3728(0)#/)9:-).&;(03"<)

!"#$%%&'()*+,-.*(/)%0/1#'123%#(-0%455567

SELECT id, post_author AS 'sioc:has_creator->user', post_title AS 'dc:title', post_content AS 'sioc:content', post_date AS 'dcterms:modified^^xsd:dateTime‘, post_modified AS 'dcterms:created^^xsd:dateTime'

FROM posts WHERE post_status='publish‘ (AND id=xxx)

SELECT post_id id, tag_label AS 'tag:taggedWithTag‘ FROM post2tag INNER JOIN tag ON(post2tag.tag_id=tag.tag_id) (WHERE id=xxx)

SELECT post_id id, category_id AS 'belongsToCategory->category‘ FROM post2cat (WHERE id=xxx)



D2R Server

• a tool for publishing the data from relational databases on the Web

116



D2R Server

117

map:Conference a d2rq:ClassMap;

d2rq:dataStorage map:Database1.

d2rq:class :Conference;

d2rq:uriPattern "http://conferences.org/comp/confno@@Conferences.ConfID@@";

.

map:eventTitle a d2rq:PropertyBridge;

d2rq:belongsToClassMap map:Conference;

d2rq:property :eventTitle;

d2rq:column "Conferences.Name";

d2rq:datatype xsd:string;

.

• D2RQ mapping excerpt


http://conferences.org/comp/confno@@Conferences.ConfID@@

http://conferences.org/comp/confno@@Conferences.ConfID@@


D2R Server

• supports auto-generation of mapping files

• extracted from database structure

• good starting point

• requires adaption for domain-specific vocabulary

• supports dumping databases to RDF files

118



Virtuoso RDF Views

• transforms the result of SQL SELECT statements into RDF

• mapping steps

• define RDFS class IRIs for each table

• define construction of subject IRIs from primary key column values

• define construction of predicate IRIs from each non-key column

119



OAI2LOD Server

• publishes metadata from arbitrary OAI-PMH endpoints as linked data on the Web

• provides a simple linking framework

120



OAI2LOD Server

• Sample harvesting configuration:

121

<> a oai2lod:Server;

rdfs:label "Example OAI2LOD Server";

oai2lod:port 2020;

oai2lod:baseURI <http://localhost:2020/>;

oai2lod:publishes <oai1>;

oai2lod:linkedWith <link1>;

.

<oai1> a oai2lod:OAIServer;

oai2lod:serverURL <http://oai-bdb.onb.ac.at/Script/oai2.aspx>;

oai2lod:metadataPrefix "oai_dc";

oai2lod:styleSheet "xsl/oai_dc2rdf_xml.xsl";

oai2lod:maxRecords 50;

.


http://localhost:2020/

http://localhost:2020/

http://oai-bdb.onb.ac.at/Script/oai2.aspx

http://oai-bdb.onb.ac.at/Script/oai2.aspx


OAI2LOD Server

• Sample linking configuration:

122

<link1> a oai2lod:LinkedSPARQLEndpoint;

oai2lod:sparqlService <http://DBpedia.org/sparql>;

oai2lod:maxResults 5000;

oai2lod:linkingRule <lrule1>;

.

<lrule1> a oai2lod:LinkingRule;

oai2lod:sourceType <http://www.mediaspaces.info/vocab/oai-pmh.rdf#Item>;

oai2lod:sourceProperty <http://purl.org/dc/elements/1.1/subject>;

oai2lod:targetType <http://dbpedia.org/class/yago/Capital108518505>;

oai2lod:targetProperty <http://www.w3.org/2000/01/rdf-schema#label>;

oai2lod:linkingProperty <http://www.w3.org/2000/01/rdf-schema#seeAlso>;

oai2lod:similarityMetrics "uk.ac.shef.wit.simmetrics.similaritymetrics.Levenshtein";

oai2lod:minSimilarity 1.0;

.


http://DBpedia.org/sparql

http://DBpedia.org/sparql

http://www.mediaspaces.info/vocab/oai-pmh.rdf#Item

http://www.mediaspaces.info/vocab/oai-pmh.rdf#Item

http://purl.org/dc/elements/1.1/subject

http://purl.org/dc/elements/1.1/subject

http://dbpedia.org/class/yago/Capital108518505

http://dbpedia.org/class/yago/Capital108518505

http://www.w3.org/2000/01/rdf-schema#label

http://www.w3.org/2000/01/rdf-schema#label

http://www.w3.org/2000/01/rdf-schema#seeAlso

http://www.w3.org/2000/01/rdf-schema#seeAlso


SILK - Link Discovery Framework

• Supports data publishers in linking their data sets with other

• Provides a declarative Link Specification Language

• specify which links to be discovered

• specify conditions data items must fulfill in order to be linked

• implemented in Python

123



SILK - Link Discovery Framework

124

<Interlink id="countries">

<LinkType>owl:sameAs</LinkType>

<SourceDataset dataSource="dbpedia" var="a">

<RestrictTo> ?a rdf:type dbpedia:Country </RestrictTo>

</SourceDataset>

<TargetDataset dataSource="factbook" var="b"/>

...

<LinkCondition>

<AVG>

<Compare id="jaroSimilarity" weight="2">

<Param name="string1" path="?a/rdfs:label" />

<Param name="string2" path="?b/rdfs:label" />

</Compare>

<Compare id="numSimilarity">

<Param name="num1" path="?a/dbpedia:population" />

<Param name="num2" path="?b/fb:totalPopulation" />

<Param name="factor" value="2" />

</Compare>

</AVG>

</LinkCondition>

<Thresholds accept="0.9" verify="0.7" />

<Limit max="1" method="metric_value" />

<Output acceptedLinks="accepted_links.n3" verifyLinks="verify_links.n3" mode="truncate" format="n3"/>

</Interlink>



References

• A Survey of current approaches for mapping of relational databases to RDF: http://esw.w3.org/topic/Rdb2RdfXG/StateOfTheArt

• Triplify: http://triplify.org/Overview

• D2R Server: http://www4.wiwiss.fu-berlin.de/bizer/d2r-server/

• OpenLink Virtuoso: http://virtuoso.openlinksw.com/Whitepapers/html/rdf_views/virtuoso_rdf_views_example.html

• OAI2LOD Server: http://www.mediaspaces.info/tools/oai2lod

• SILK: http://www4.wiwiss.fu-berlin.de/bizer/silk/

125


http://esw.w3.org/topic/Rdb2RdfXG/StateOfTheArt

http://esw.w3.org/topic/Rdb2RdfXG/StateOfTheArt

http://triplify.org/Overview

http://triplify.org/Overview

http://www4.wiwiss.fu-berlin.de/bizer/d2r-server/

http://www4.wiwiss.fu-berlin.de/bizer/d2r-server/

http://virtuoso.openlinksw.com/Whitepapers/html/rdf_views/virtuoso_rdf_views_example.html




http://www.mediaspaces.info/tools/oai2lod

http://www.mediaspaces.info/tools/oai2lod

http://www4.wiwiss.fu-berlin.de/bizer/silk/

http://www4.wiwiss.fu-berlin.de/bizer/silk/


Contents







126



Vocabularies & Interoperability Issues

• LOD is about publishing data on the Web

• vocabularies define the terms that describe the semantics of these data (e.g., creator, title, abstract, etc.)

• we can apply the LOD principles and expose vocabularies on the Web

127




• Use URIs as names for vocabularies and terms

• Use HTTP URIs so that people (and machines) can look up those names

• When someone looks up a URI, provide useful information

• Include links (mappings) to other vocabularies

128




• Example: Dublin Core terms

129




• Example: Dublin Core terms

130




• Example: Friend of a Friend (FOAF)

131




• Example: Friend of a Friend (FOAF)

132




• Publishing vocabularies on the Web recipe

133





• Step 1: create a complete RDF/XML serialization of the vocabulary (e.g., example.rdf)

• Step 2: copy the serialization into Web Server directory

• Step3: add a .htaccess directive to the Web Server directory

134





135




• LOD and the Semantic Web provide the technologies to expose data on the Web

• exposing data in RDF and describing vocabularies in RDF/S or OWL provides data interoperability on a technical / structural level

• semantic interoperability is not given by default

136




rule-of-thumb to establish semantic interoperability

1. whenever possible, use terms from widely used vocabularies that are published on the Web in a structured, machine-readable format (RDFS or OWL)

2. if there is no such term that reflects the required semantics, re-use a semantically broader term by establishing e.g. a rdfs:subProperty relationship, refine its semantics for the purpose of your application within a new namespace, and publish it on the Web

3. if (1) and (2) are not feasible, create your own vocabulary and publish it on the Web in order to make it accessible for other users and applications; consider to define mappings to other vocabularies

137




138

Name Purpose Base Concepts/Properties

Dublin Core(http://purl.org/dc/terms)

General / Documents RDFS 22 / 55

Friend of a Friend (FOAF)(http://xmlns.com/foaf/0.1/)

Contacts / Communication OWL 12 / 54

VCard Ontology(http://www.w3.org/2006/vcard/ns#)


Description of a Project (DOAP)(http://usefulinc.com/ns/doap# ) Projects RDFS 7 / 30


http://purl.org/dc/terms

http://purl.org/dc/terms

http://xmlns.com/foaf/0.1/

http://xmlns.com/foaf/0.1/

http://www.w3.org/2006/vcard/ns#

http://www.w3.org/2006/vcard/ns#

http://usefulinc.com/ns/doap#

http://usefulinc.com/ns/doap#



139

Name Purpose Base Concepts/Properties

Semantically Interlinked Online Communities (SIOC)

(http://rdfs.org/sioc/ns#)


Nepomuk Message Ontology (NMO)(http://www.semanticdesktop.org/ontologies/

2007/03/22/nmo# )

Contacts / Communication RDFS 7 / 23

GeoNames Ontology(http://www.geonames.org/ontology#) Locations OWL 7 / 18

Music Ontology(http://purl.org/ontology/mo/ ) Multimedia OWL 53 / 131


http://rdfs.org/sioc/ns#

http://rdfs.org/sioc/ns#

http://www.semanticdesktop.org/ontologies/2007/03/22/nmo#




http://www.geonames.org/ontology#

http://www.geonames.org/ontology#

http://purl.org/ontology/mo/

http://purl.org/ontology/mo/



140

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+#$,-#,)*

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.)/,/*AB@0A:AQ42*=QRQ9

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>-"7;&'"N*Q)6;&%

.)/,/*+0A*>-"7;&'"')(2*@)-"(67)*F)&(;$)$$;&8%#")'*

.FS@99



References

• Miles et al.: Best Practices Recipes for Publishing RDF Vocabularies, Available at: http://www.w3.org/TR/swbp-vocab-pub/

• Heery and Patel 2004: Application profiles: mixing and matching metadata schemes. Available at: http://www.ariadne.ac.uk/issue25/app-profiles/

• Haslhofer and Klas 2009: A Survey of approaches for achieving metadata interoperability. To be published in ACM Computing Surveys Q4/2009. Available on request.

• Haslhofer and Schandl 2009: Interweaving OAI-PMH metadata with the Linked Data Cloud. To be published in International Journal of Metadata, Semantics, and Ontologies. Available on request.

141


http://www.w3.org/TR/swbp-vocab-pub/

http://www.w3.org/TR/swbp-vocab-pub/

http://www.ariadne.ac.uk/issue25/app-profiles/

http://www.ariadne.ac.uk/issue25/app-profiles/


Contents







142



Demo 1 - browsing and querying DBPedia

• http://dbpedia.org/resource/Hallstatt_culture

• http://dbpedia.org/snorql

• http://lookup.dbpedia.org

143




http://dbpedia.org/sparql

http://dbpedia.org/sparql

http://lookup.dbpedia.org

http://lookup.dbpedia.org


Demo 2 - cURLing the LIBRIS catalogue

• LIBRIS = The Swedish Union Catalog

• Starting point: http://libris.kb.se/bib/10432900

144


http://libris.kb.se/bib/10432900

http://libris.kb.se/bib/10432900


Demo 3 - exposing MySQL DB using D2R

• sample database: http://dev.mysql.com/doc/world-setup/en/world-setup.html

145


http://dev.mysql.com/doc/world-setup/en/world-setup.html





Demo 4 - sample OAI2LOD instances

• http://www.mediaspaces.info/tools/oai2lod/

146


http://www.mediaspaces.info/tools/oai2lod/

http://www.mediaspaces.info/tools/oai2lod/


Demo 5 - RDF Viewers

• Zitgist: http://dataviewer.zitgist.com/

• Disco: http://www4.wiwiss.fu-berlin.de/rdf_browser/

• OpenLink Data Explorer: http://demo.openlinksw.com/rdfbrowser2

147


http://dataviewer.zitgist.com

http://dataviewer.zitgist.com

http://www4.wiwiss.fu-berlin.de/rdf_browser/

http://www4.wiwiss.fu-berlin.de/rdf_browser/

http://demo.openlinksw.com/rdfbrowser2





Known / Open Issues

• Automatic linking is non-trival and domain specific

• how to deal with false positives?

• precision / recall of existing approaches?

• Nobody can guarantee the (long-term) availability of LOD resources

• what to do when a resource disappears?

• annoying for humans / problematic for applications

• Licensing

148



Summary

• Linked Data is about publishing and interlinking public interest data on the Web

• Other applications can access these data with common Web technologies

• It is still research, with lots of construction areas, but within its two year (!!!) history it has attracted quite a lot of interest

• It is an exciting research field to work on...

149



Summary

150



Questions / Discussion

151
