Linked Data Tutorial

Linked Data Tutorial
Linked Data Tutorial @ Vlaams Theater Instituut Brussels, 03/2009 bernhard.haslhofer@univie.ac.at Bernhard Haslhofer, Linked Data Tutorial Friday, March 6, 2009
Contents • Motivation for Linked Open Data (LOD) • Base Technologies • The Linked Data Principles • Publishing Solutions and Tools • Vocabularies & Interoperability Issues • Demos + Discussion Bernhard Haslhofer, Linked Data Tutorial 2 Friday, March 6, 2009
How do we look up information about things? Bernhard Haslhofer, Linked Data Tutorial 3 Friday, March 6, 2009
... about this book? Bernhard Haslhofer, Linked Data Tutorial 4 Friday, March 6, 2009
... about this play? Bernhard Haslhofer, Linked Data Tutorial 5 Friday, March 6, 2009
... about these concepts? Bernhard Haslhofer, Linked Data Tutorial 6 Friday, March 6, 2009
... about things? ...that book? ...this play? ...these concepts? we look up their names Metamorphosis Effi Briest Love / Hate and see what we can find out Bernhard Haslhofer, Linked Data Tutorial 7 Friday, March 6, 2009
An Example Bernhard Haslhofer, Linked Data Tutorial 8 Friday, March 6, 2009
The Hallstatt culture Bernhard Haslhofer, Linked Data Tutorial 9 Friday, March 6, 2009
formerly Controlled Vocabulary Bernhard Haslhofer, Linked Data Tutorial 10 Friday, March 6, 2009
formerly Metadata Identifier Bernhard Haslhofer, Linked Data Tutorial 11 Friday, March 6, 2009
then Identifier Metadata Controlled Vocabulary Bernhard Haslhofer, Linked Data Tutorial 12 Friday, March 6, 2009
now Bernhard Haslhofer, Linked Data Tutorial 13 Friday, March 6, 2009
If information is not available on the Web, people tend to ignore it. Bernhard Haslhofer, Linked Data Tutorial 14 Friday, March 6, 2009
Current Situation Web Web Server JDBC HTML Database Bernhard Haslhofer, Linked Data Tutorial 15 Friday, March 6, 2009
The current Web is a Web of Documents intended for human interpretation. Bernhard Haslhofer, Linked Data Tutorial 16 Friday, March 6, 2009
Database Database Database The data are still locked in closed silos. Database Database Database Bernhard Haslhofer, Linked Data Tutorial 17 Friday, March 6, 2009
Other applications can not access and process these data unless... Bernhard Haslhofer, Linked Data Tutorial 18 Friday, March 6, 2009
Existing Approaches CD-ROM FTP REST OAI-PMH Web Services SRU/SRQ SOAP OAI-ORE RSS WSDL Atom UDDI JSON CD-ROM RPC RMI CORBA Z39.50 DCOM Bernhard Haslhofer, Linked Data Tutorial 19 Friday, March 6, 2009
The linked data vision is to... Bernhard Haslhofer, Linked Data Tutorial 20 Friday, March 6, 2009
Documents Data Database Bernhard Haslhofer, Linked Data Tutorial Friday, March 6, 2009
• 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 Bernhard Haslhofer, Linked Data Tutorial 22 Friday, March 6, 2009
make it possible for applications to look up (meta)data ... Bernhard Haslhofer, Linked Data Tutorial 23 Friday, March 6, 2009
... about things ...that book? ...this play? ...these concepts? by looking up their names http://dbpedia.org/resource/ Love http://dbpedia.org/resource/ http://dbpedia.org/resource/ The_Metamorphosis Effi_Briest http://dbpedia.org/resource/ Hatred on the Web Bernhard Haslhofer, Linked Data Tutorial 24 Friday, March 6, 2009
To do so, we need some technology Bernhard Haslhofer, Linked Data Tutorial 25 Friday, March 6, 2009
Uniform Resource Identifier (URI) • Names (Identifiers) for resources in an open environment • dereferencable URI = HTTP URI (URL) http://dbpedia.org/resource/ Hallstatt_culture Bernhard Haslhofer, Linked Data Tutorial 26 Friday, March 6, 2009
Resource Description Framework (RDF) • a model for representing metadata on the Web • in the form of statements (triples) “The Hallstatt culture t abstrac : was ...” p dbppro rdfs: label http://dbpedia.org/resource/ “Hallstatt culture” Hallstatt_culture skos:s ubject http:// dbpedia.org/resource/ Category:Iron_Age_Europe Bernhard Haslhofer, Linked Data Tutorial 27 Friday, March 6, 2009
RDF/XML, N3, Turtle, etc. • for exchanging RDF data • serialization & de-serialization <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> Bernhard Haslhofer, Linked Data Tutorial 28 Friday, March 6, 2009
RDFS & OWL • languages for describing vocabularies rdf: Property rdf: type rdf: type rdf: type dbpprop: abstract skos: subject rdfs: label Bernhard Haslhofer, Linked Data Tutorial 29 Friday, March 6, 2009
Simple Knowledge Organization System (SKOS) • a language for describing controlled vocabularies “Iron Age “Hallstatt Period” “Hallstatt Culture” Europe” skos:prefLabel skos:prefLabel skos:altLabel “La Tène Period” skos:narrower dbpedia:Category: xyz: HallstattCulture skos:prefLabel Iron_Age_Europe skos:narrower xyz: LateneCulture Bernhard Haslhofer, Linked Data Tutorial 30 Friday, March 6, 2009
SPARQL • a query language & protocol for accessing RDF data via the Web SELECT ?uri WHERE { ?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe>. } Bernhard Haslhofer, Linked Data Tutorial 31 Friday, March 6, 2009
The vision is becoming reality... Bernhard Haslhofer, Linked Data Tutorial 32 Friday, March 6, 2009
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 “ ” @jp; skos:subject dbpedia:Category:Iron_Age_Europe; ... Bernhard Haslhofer, Linked Data Tutorial 33 Friday, March 6, 2009
<http://dbpedia.org/resource/Hallstatt_culture > ... p:hasPhotoCollection <http://www4.wiwiss.fu-berlin.de/flickrwrappr/ photos/Hallstatt_culture>; ... Bernhard Haslhofer, Linked Data Tutorial 34 Friday, March 6, 2009
Library of Congress Subject Headings Bernhard Haslhofer, Linked Data Tutorial 35 Friday, March 6, 2009
Friday, March 6, 2009
The LOD idea in brief • expose data on the Web, not just documents • interlink these data with those of other data sources Bernhard Haslhofer, Linked Data Tutorial 37 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 38 Friday, March 6, 2009
“Stop hugging your data” Sir Tim Berners-Lee, 2009 (c) Paul Miller, http://www.slideshare.net/ cloudofdata/toward-the-data-cloud Friday, March 6, 2009
The Semantic Web Layer Cake User Interface & Applications Trust Proof Unifying Logic Vocabulary: Ontology: Rules: SKOS OWL RIF Query: SPARQL Crypto RDF-S Data Interchange: RDF XML URI Unicode Bernhard Haslhofer, Linked Data Tutorial 41 Friday, March 6, 2009
From a Database point of view Database Domain Semantic Web Relational Model URI, RDF (Tables) SQL DDL RDFS, OWL (Create Table table-name ...) SQL Query Language SPARQL (Select * from ...) Bernhard Haslhofer, Linked Data Tutorial 42 Friday, March 6, 2009
Uniform Resource Identifiers (URI) • Unambiguous name for “something” • for a digital resource http://dbpedia.org/resource/ • for a concept within a vocabulary Hallstatt_culture • etc.. • “A URI is a compact sequence of characters that identifies an abstract or physical resource” [RFC 3986] http://dbpedia.org/resource/ Hallstatt Bernhard Haslhofer, Linked Data Tutorial 43 Friday, March 6, 2009
Uniform Resource Identifiers (URI) • “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 Bernhard Haslhofer, Linked Data Tutorial 44 Friday, March 6, 2009
Uniform Resource Identifiers (URI) • 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) Bernhard Haslhofer, Linked Data Tutorial 45 Friday, March 6, 2009
Uniform Resource Identifiers (URI) • Generic syntax - a hierarchical sequence of components URI = scheme “:” hier-path [ “?” query ] [ “#” fragment ] foo://example.com:8042/over/there?name=ferret#nose _/ ________________/_________/ _________/ __/ | | | | | scheme authority path query fragment | ______________________|_ // urn:example:animal:ferret:nose Bernhard Haslhofer, Linked Data Tutorial 46 Friday, March 6, 2009
Uniform Resource Identifiers (URI) • Example URIs: ftp://ftp.is.co.za/rfc/rfc1808.txt http://www.ietf.org/rfc/rfc2396.txt ldap://[2001:db8::7]/c=GB?objectClass?one mailto:John.Doe@example.com news:comp.infosystems.www.servers.unix tel:+1-816-555-1212 urn:oasis:names:specification:docbook:dtd:xml:4.1.2 Bernhard Haslhofer, Linked Data Tutorial 47 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 48 Friday, March 6, 2009
Resource Description Framework (RDF) • The basic structural element of RDF is the statement rdfs: label http://dbpedia.org/resource/ “Hallstatt culture” Hallstatt_culture skos:s ubject http://dbpedia.org/resource/ Category:Iron_Age_Europe Subject Predicate Object Subject Property Value Bernhard Haslhofer, Linked Data Tutorial 50 Friday, March 6, 2009
Resource Description Framework (RDF) • 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 Bernhard Haslhofer, Linked Data Tutorial 51 Friday, March 6, 2009
Resource Description Framework (RDF) • Literals can be plain or typed using arbitrary datatypes • It is recommended to use XML Schema datatypes [XMLS2] rdfs: label http://dbpedia.org/resource/ “Hallstatt” Hallstatt geo:lo ng “13.646667”^^<http:// www.w3.org/2001/ XMLSchema#float> Bernhard Haslhofer, Linked Data Tutorial 52 Friday, March 6, 2009
Resource Description Framework (RDF) • Support for multilingual labels • Plain literals may have a language tag, as defined by RFC 3066 “ ( l : labe )”@jp rdfs rdfs: label http://dbpedia.org/resource/ “Hallstatt”@de Hallstatt rdfs:la bel “Гальштат”@ru Bernhard Haslhofer, Linked Data Tutorial 53 Friday, March 6, 2009
Resource Description Framework (RDF) • 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 http://www.ex.com/ http://www.ex.com/#address staff#85740 http://www.ex.com/#zipcode http://www.ex.com/#city http://www.ex.com/#street http://www.ex.com/#state quot;01730quot; quot;Bedfordquot; quot;1501 Grant quot;Massachusettsquot; Avenuequot; Bernhard Haslhofer, Linked Data Tutorial 54 Friday, March 6, 2009
Resource Description Framework (RDF) • Containers allow to describe groups of things • Bag (unordered set), Seq (ordered set), Alt (choice) http://www.ex.com/ http://www.w3.org/1999/02/22-rdf- courses#6.001 syntax-ns#Bag http://www.ex.com/students#students http://www.ex.com/students#Amy http://www.w3.org/1999/02/22-rdf-syntax-ns#type http://www.w3.org/1999/02/22-rdf-syntax-ns#_1 http://www.ex.com/ http://www.w3.org/1999/02/22-rdf-syntax-ns#_2 students#Mohamed http://www.w3.org/1999/02/22-rdf-syntax-ns#_3 http://www.w3.org/1999/02/22-rdf-syntax-ns#_4 http://www.ex.com/students#Johann blank node http://www.ex.com/students#Maria Bernhard Haslhofer, Linked Data Tutorial 55 Friday, March 6, 2009
Resource Description Framework (RDF) • Collections allow the definition of closed containers • define the exact set of items in a collection http://www.ex.com/ courses#6.001 http://www.ex.com/students#students http://www.w3.org/1999/02/22-rdf-syntax-ns#first http://www.ex.com/students#Amy http://www.w3.org/1999/02/22-rdf-syntax-ns#rest http://www.w3.org/1999/02/22-rdf-syntax-ns#first http://www.ex.com/ students#Mohamed http://www.w3.org/1999/02/22-rdf-syntax-ns#rest http://www.w3.org/1999/02/22-rdf-syntax-ns#first http://www.ex.com/students#Johann http://www.w3.org/1999/02/22-rdf-syntax-ns#rest http://www.w3.org/1999/02/22-rdf- syntax-ns#nil Bernhard Haslhofer, Linked Data Tutorial 56 Friday, March 6, 2009
Resource Description Framework (RDF) • RDF can be serialized using various syntax formats: <?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/XML </rdf:Description> Bernhard Haslhofer, Linked Data Tutorial 57 Friday, March 6, 2009
Resource Description Framework (RDF) • RDF can be serialized using various syntax formats: @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 > ; Turtle / N3 rdfs:label “Hallstatt culture” . Bernhard Haslhofer, Linked Data Tutorial 58 Friday, March 6, 2009
Resource Description Framework (RDF) • Reification • allows to describe other statements; i.e. make statements about other statements • rarely used in practice Bernhard Haslhofer, Linked Data Tutorial 59 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 61 Friday, March 6, 2009
RDF Schema (RDFS) • classes and subclass relationships rdfs: Class rdf:type rdf:type yago: yago: City CitiesAndTownsInUpperAustria rdfs: subClassOf rdf:type http://dbpedia.org/resource/ Hallstatt Bernhard Haslhofer, Linked Data Tutorial 62 Friday, March 6, 2009
RDF Schema (RDFS) • properties and subPropertyOf relationships rdf: Property rdf:type rdf:type dcterms: description dbProp: abstract rdfs: subPropertyOf Note: in reality, dbpedia: abstract is no subject of Bernhard Haslhofer, Linked Data Tutorial 63 dcterms; description Friday, March 6, 2009
RDF Schema (RDFS) • domain and range relationships rdfs: Class rdf: type xyz: Article rdfs: domain dbProp: abstract rdfs: range xsd: string Bernhard Haslhofer, Linked Data Tutorial 64 Friday, March 6, 2009
RDF Schema (RDFS) • comments: rdfs: comment • human-readable names for resources: rdfs: label • machine-readable information: rdfs: seeAlso, rdfs: isDefinedBy Bernhard Haslhofer, Linked Data Tutorial 65 Friday, March 6, 2009
RDF Schema (RDFS) • Shortcomings: • no cardinality constraints on properties • no inverse / transitive / symmetric properties • no union / disjoint / enumeration classes Bernhard Haslhofer, Linked Data Tutorial 66 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 68 Friday, March 6, 2009
Web Ontology Language (OWL) • 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 rdfs: Class rdfs: subClassOf owl: Class owl: Thing rdfs: subClassOf rdf:type rdf:type http://dbpedia.org/resource/ dbpedia-owl: Place Hallstatt Bernhard Haslhofer, Linked Data Tutorial 69 Friday, March 6, 2009
Web Ontology Language (OWL) • DatatypeProperty: properties whose value is a literal • ObjectProperty: properties whose value is an individual owl: rdf:type rdfs: range xsd: string DatatypeProperty dbPedia-owl: id rdfs: subClassOf rdfs: domain dbPedia-owl: rdf: Property WorldHeritageSite dbPedia-owl: rdf:type rdfs: domain rdfs: subClassOf region owl: dbpedia-owl: rdfs: range ObjectProperty PopulatedPlace Bernhard Haslhofer, Linked Data Tutorial 70 Friday, March 6, 2009
Web Ontology Language (OWL) • owl: equivalentClass states that two classes are equivalent, i.e., they have the same instances owl: equivalentClass dbpedia: Car dbpedia: Automobile Note: DBpedia actually uses dbpedia: redirect Bernhard Haslhofer, Linked Data Tutorial 71 Friday, March 6, 2009
Web Ontology Language (OWL) • owl: equivalentProperty states that two properties are equivalent; they relate one individual to the same set of other individuals owl: equivalentProperty myOnt: abstract dbpprop: abstract Bernhard Haslhofer, Linked Data Tutorial 72 Friday, March 6, 2009
Web Ontology Language (OWL) • owl:sameAs states that two individuals are the same owl: sameAs http://dbpedia.org/resource/ fbase: Hallstatt culture Hallstatt_culture Bernhard Haslhofer, Linked Data Tutorial 73 Friday, March 6, 2009
Web Ontology Language (OWL) • 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) Bernhard Haslhofer, Linked Data Tutorial 74 Friday, March 6, 2009
Web Ontology Language (OWL) • 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 Bernhard Haslhofer, Linked Data Tutorial 75 Friday, March 6, 2009
Web Ontology Language (OWL) • 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 = ∅) Bernhard Haslhofer, Linked Data Tutorial 76 Friday, March 6, 2009
Simple Knowledge Organization System (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 Bernhard Haslhofer, Linked Data Tutorial 78 Friday, March 6, 2009
Simple Knowledge Organization System (SKOS) • vocabulary terms are represented as concepts identified by URIs skos: Concept rdf: type rdf: type dbpedia: Category: xyz: HallstattCulture Iron_Age_Europe Bernhard Haslhofer, Linked Data Tutorial 79 Friday, March 6, 2009
Simple Knowledge Organization System (SKOS) • concepts have preferred, alternate & hidden labels • label is either preferred or alternate or hidden; one per language “Hallstatt Period@en” bel a refL :p kos s l fLabe “Hallstatt Kultur@de” s: pre sko xyz: HallstattCulture skos: altLab el “Hallstatt Culture@en” Bernhard Haslhofer, Linked Data Tutorial 80 Friday, March 6, 2009
Simple Knowledge Organization System (SKOS) • concepts can be organized in hierarchies by (the inverse) skos: broader or skos: narrower relationships dbpedia: Category: dbpedia: Category: Iron_Age Prehistoric_Europe skos: broader skos: broader skos: narrower dbpedia: Category: xyz: HallstattCulture Iron_Age_Europe Note: in DBPedia this narrower rel. does not exist Bernhard Haslhofer, Linked Data Tutorial 81 Friday, March 6, 2009
Simple Knowledge Organization System (SKOS) • concepts can be associated by non-hierarchical (non- transitive) skos:related properties skos: related xyz: HallstattCulture xyz: HallstattCivilization Bernhard Haslhofer, Linked Data Tutorial 82 Friday, March 6, 2009
Simple Knowledge Organization System (SKOS) • 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 Bernhard Haslhofer, Linked Data Tutorial 83 Friday, March 6, 2009
Simple Knowledge Organization System (SKOS) • concepts can be defined as part of well-defined concept schemes (thesauri, classification schemes) dc:title “Archeology Thesaurus” ex: archeologyThesaurus dc:creator “John Doe” skos: inScheme skos: inScheme xyz: HallstattCulture xyz: HallstattCivilization Bernhard Haslhofer, Linked Data Tutorial 84 Friday, March 6, 2009
Simple Knowledge Organization System (SKOS) • 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 • .... Bernhard Haslhofer, Linked Data Tutorial 85 Friday, March 6, 2009
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) Bernhard Haslhofer, Linked Data Tutorial 87 Friday, March 6, 2009
SPARQL • a simple query example SELECT ?uri WHERE { ?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe>. } uri ... dbpedia: Hallstatt_culture ... Bernhard Haslhofer, Linked Data Tutorial 88 Friday, March 6, 2009
SPARQL • querying multiple variables SELECT ?uri ?abstract WHERE { ?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe>. ?uri dbpprop:abstract ?abstract . } uri abstract ... dbpedia: Hallstatt_culture The Hallstatt culture was the... dbpedia: Hallstatt_culture Гальшта́тская культу́ра ... Bernhard Haslhofer, Linked Data Tutorial 89 Friday, March 6, 2009
SPARQL • querying and filtering literal values 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 Bernhard Haslhofer, Linked Data Tutorial 90 Friday, March 6, 2009
SPARQL • optional graph patterns SELECT ?uri ?label ?image WHERE { ?uri rdfs:label ?label . ?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe> . OPTIONAL { ?uri foaf:img ?image }. } Bernhard Haslhofer, Linked Data Tutorial 91 Friday, March 6, 2009
SPARQL • optional graph patterns with constraints SELECT ?uri ?label ?image WHERE { ?uri rdfs:label ?label . ?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe> . OPTIONAL { ?uri foaf:img ?image . FILTER regex(?image, “jpg”, “i”) . }. } Bernhard Haslhofer, Linked Data Tutorial 92 Friday, March 6, 2009
SPARQL • matching alternatives SELECT ?uri ?classification WHERE { ?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe> . { ?uri rdf:type ?classification . } UNION { ?uri skos:subject ?classification . } } Bernhard Haslhofer, Linked Data Tutorial 93 Friday, March 6, 2009
SPARQL • solution modifiers SELECT ?uri ?name WHERE { ?uri skos:subject <http://dbpedia.org/resource/Category:Iron_Age_Europe> . ?uri rdfs:label ?name } ORDER BY ?name LIMIT 10 OFFSET 5 Bernhard Haslhofer, Linked Data Tutorial 94 Friday, March 6, 2009
SPARQL • Other SPARQL features: • rich set of FILTER expressions (see xquery functions) • CONSTRUCT, DESCRIBE, ASK queries • Named Graphs Bernhard Haslhofer, Linked Data Tutorial 95 Friday, March 6, 2009
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. Bernhard Haslhofer, Linked Data Tutorial 97 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 98 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 100 Friday, March 6, 2009
Use HTTP URIs.... http://dbpedia.org/resource/ Hallstatt http://dbpedia.org/resource/ Hallstatt_culture http://dbpedia.org/resource/ Category:World_Heritage_Sites_in_Austria Bernhard Haslhofer, Linked Data Tutorial 101 Friday, March 6, 2009
Provide useful information ... for humans Bernhard Haslhofer, Linked Data Tutorial 102 Friday, March 6, 2009
Provide useful information ... for machines <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 “ ” @jp; skos:subject dbpedia:Category:Iron_Age_Europe; ... Bernhard Haslhofer, Linked Data Tutorial 103 Friday, March 6, 2009
Provide useful information for humans and machines • return different HTTP responses depending on HTTP- Accept-Header Bernhard Haslhofer, Linked Data Tutorial 104 Friday, March 6, 2009
Provide useful information for humans and machines • best practice: also assign names (URIs) to various representations http://dbpedia.org/resource/ Hallstatt_culture Accept: application/rdf+xml Accept: text/html http://dbpedia.org/data/ http://dbpedia.org/page/ Hallstatt_culture.rdf Hallstatt_culture Bernhard Haslhofer, Linked Data Tutorial 105 Friday, March 6, 2009
Include links dbpprop: hasPhotoCollection http://www4.wiwiss.fu-berlin.de/ flickrwrappr/photos/Hallstatt_culture http://dbpedia.org/resource/ Hallstatt_culture owl: sameAs http://rdf.freebase.com/ns/guid. 9202a8c04000641f8000000000239c44 Bernhard Haslhofer, Linked Data Tutorial 106 Friday, March 6, 2009
Include links • other common properties • rdfs: seeAlso • foaf: knows • foaf: based_near • foaf: topic_interest Bernhard Haslhofer, Linked Data Tutorial 107 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 108 Friday, March 6, 2009
Benefit • Clients can easily look up names and retrieve information and follow the links Bernhard Haslhofer, Linked Data Tutorial 109 Friday, March 6, 2009
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/ Bernhard Haslhofer, Linked Data Tutorial 110 Friday, March 6, 2009
Relational Databases Triplify D2R Server Virtuoso RDF Views Scripting languages Java Middleware Solution Technology (PHP) - Yes Yes SPARQL Endpoint SQL RDF based RDF based Mapping Language Manual Semi-automatic Manual Mapping Generation Medium-high medium high Scalability (but no SPARQL) (c) Sören Auer, http://www.slideshare.net/soeren1611/linked-data- Bernhard Haslhofer, Linked Data Tutorial 112 tutorial-presentation-955375 Friday, March 6, 2009
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) Bernhard Haslhofer, Linked Data Tutorial 113 Friday, March 6, 2009
Triplify • Configuration • number of SQL queries selecting information, which should be made publicly available SELECT id, name AS ‘foaf:name’ FROM users Bernhard Haslhofer, Linked Data Tutorial 114 Friday, March 6, 2009
Triplify !quot;quot;#$%&'()'*()+,-).&'*)/0&12(3')4.#quot;'5)6%'*)&)3728(0)#/) 9:-).&;(03quot;<) !quot;#$%%&'()*+,-.*(/)%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) Bernhard Haslhofer, Linked Data Tutorial 115 Friday, March 6, 2009
D2R Server • a tool for publishing the data from relational databases on the Web Bernhard Haslhofer, Linked Data Tutorial 116 Friday, March 6, 2009
D2R Server • D2RQ mapping excerpt map:Conference a d2rq:ClassMap; d2rq:dataStorage map:Database1. d2rq:class :Conference; d2rq:uriPattern quot;http://conferences.org/comp/confno@@Conferences.ConfID@@quot;; . map:eventTitle a d2rq:PropertyBridge; d2rq:belongsToClassMap map:Conference; d2rq:property :eventTitle; d2rq:column quot;Conferences.Namequot;; d2rq:datatype xsd:string; . Bernhard Haslhofer, Linked Data Tutorial 117 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 118 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 119 Friday, March 6, 2009
OAI2LOD Server • publishes metadata from arbitrary OAI-PMH endpoints as linked data on the Web • provides a simple linking framework Bernhard Haslhofer, Linked Data Tutorial 120 Friday, March 6, 2009
OAI2LOD Server • Sample harvesting configuration: <> a oai2lod:Server; rdfs:label quot;Example OAI2LOD Serverquot;; 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 quot;oai_dcquot;; oai2lod:styleSheet quot;xsl/oai_dc2rdf_xml.xslquot;; oai2lod:maxRecords 50; . Bernhard Haslhofer, Linked Data Tutorial 121 Friday, March 6, 2009
OAI2LOD Server • Sample linking configuration: <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 quot;uk.ac.shef.wit.simmetrics.similaritymetrics.Levenshteinquot;; oai2lod:minSimilarity 1.0; . Bernhard Haslhofer, Linked Data Tutorial 122 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 123 Friday, March 6, 2009
SILK - Link Discovery Framework <Interlink id=quot;countriesquot;> <LinkType>owl:sameAs</LinkType> <SourceDataset dataSource=quot;dbpediaquot; var=quot;aquot;> <RestrictTo> ?a rdf:type dbpedia:Country </RestrictTo> </SourceDataset> <TargetDataset dataSource=quot;factbookquot; var=quot;bquot;/> ... <LinkCondition> <AVG> <Compare id=quot;jaroSimilarityquot; weight=quot;2quot;> <Param name=quot;string1quot; path=quot;?a/rdfs:labelquot; /> <Param name=quot;string2quot; path=quot;?b/rdfs:labelquot; /> </Compare> <Compare id=quot;numSimilarityquot;> <Param name=quot;num1quot; path=quot;?a/dbpedia:populationquot; /> <Param name=quot;num2quot; path=quot;?b/fb:totalPopulationquot; /> <Param name=quot;factorquot; value=quot;2quot; /> </Compare> </AVG> </LinkCondition> Bernhard Haslhofer, Linked Data Tutorial 124 <Thresholds accept=quot;0.9quot; verify=quot;0.7quot; /> Friday, March 6, 2009
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/ Bernhard Haslhofer, Linked Data Tutorial 125 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 127 Friday, March 6, 2009
Vocabularies & Interoperability Issues • 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 Bernhard Haslhofer, Linked Data Tutorial 128 Friday, March 6, 2009
Vocabularies & Interoperability Issues • Example: Dublin Core terms Bernhard Haslhofer, Linked Data Tutorial 129 Friday, March 6, 2009
Vocabularies & Interoperability Issues • Example: Dublin Core terms Bernhard Haslhofer, Linked Data Tutorial 130 Friday, March 6, 2009
Vocabularies & Interoperability Issues • Example: Friend of a Friend (FOAF) Bernhard Haslhofer, Linked Data Tutorial 131 Friday, March 6, 2009
Vocabularies & Interoperability Issues • Example: Friend of a Friend (FOAF) Bernhard Haslhofer, Linked Data Tutorial 132 Friday, March 6, 2009
Vocabularies & Interoperability Issues • Publishing vocabularies on the Web recipe Bernhard Haslhofer, Linked Data Tutorial 133 Friday, March 6, 2009
Vocabularies & Interoperability Issues • Publishing vocabularies on the Web recipe • 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 Bernhard Haslhofer, Linked Data Tutorial 134 Friday, March 6, 2009
Vocabularies & Interoperability Issues • Publishing vocabularies on the Web recipe Bernhard Haslhofer, Linked Data Tutorial 135 Friday, March 6, 2009
Vocabularies & Interoperability Issues • 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 Bernhard Haslhofer, Linked Data Tutorial 136 Friday, March 6, 2009
Vocabularies & Interoperability Issues 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 Bernhard Haslhofer, Linked Data Tutorial 137 Friday, March 6, 2009
Vocabularies & Interoperability Issues Concepts/ Name Purpose Base Properties Dublin Core General / RDFS 22 / 55 (http://purl.org/dc/terms) Documents Friend of a Friend (FOAF) Contacts / OWL 12 / 54 (http://xmlns.com/foaf/0.1/) Communication VCard Ontology Contacts / OWL 5 / 54 (http://www.w3.org/2006/vcard/ns#) Communication Description of a Project (DOAP) Projects RDFS 7 / 30 (http://usefulinc.com/ns/doap# ) Bernhard Haslhofer, Linked Data Tutorial 138 Friday, March 6, 2009
Vocabularies & Interoperability Issues Concepts/ Name Purpose Base Properties Semantically Interlinked Online Communities Contacts / (SIOC) OWL 11 / 53 Communication (http://rdfs.org/sioc/ns#) Nepomuk Message Ontology (NMO) Contacts / (http://www.semanticdesktop.org/ontologies/ RDFS 7 / 23 Communication 2007/03/22/nmo# ) GeoNames Ontology Locations OWL 7 / 18 (http://www.geonames.org/ontology#) Music Ontology Multimedia OWL 53 / 131 (http://purl.org/ontology/mo/ ) Bernhard Haslhofer, Linked Data Tutorial 139 Friday, March 6, 2009
Vocabularies & Interoperability Issues !quot;#$%& !quot;#$%&304$$5$), !$,+6!quot;#$%&304$$5$), '$(quot;)(*%*+,*quot;) !quot;#$%#&%'()%* >?(quot;&#6quot;*4)quot;#%#quot;#* !quot;#$#%&'()*# 4)quot;#%#quot;#*4)quot;#: +#$,-#,) 4;%)< +#$,-#,)* -$.*)*,*quot;)& 4)quot;#*4;%)< .)/,/*01+2*34+2* .)/,/*@A4B* 4#CC'$, .)/,/*40=9 /+)01+0$2 54+*!67)8#9 >?(quot;&#6quot;*4;%)<9 H<;?#<*A;$6)Cquot;-#<*4;%)< !quot;#$%#&%'()%* .)/,/*AB@0A:AQ42*=QRQ9 4)quot;#%#quot;#*!67)8# .)/,/*@A2*KGB2* 4)quot;#%#quot;#* !.#$#!(,*-*,*# 4)quot;#%#quot;#*=&#8)D;&E 40@!9 A&;((D#<E2* MN?&'%*4)quot;#%#quot;#* .)/,/*4FGH:IJ2*4GK!2*0>B!9 7(8$5$2 !67)8#*4#CC'$, !N(quot;)8 .)/,/*4FGH:O2 >CC<'6#quot;';$*F&;L'<) KP:>$Nquot;'8)9 .)/,/*@A*A;<<)6quot;';$*F&;L'<)9 P#<-)*G$6;%'$,*!67)8# .)/,/*B!0:S;&8(2*Q=A:!C)6'L'6#quot;';$(9 A;$quot;&;<<)%*P;6#?-<#&N B$(quot;#$6)* !+#$#!(,*-*,* .)/,/*+A!M2*@AA2*4)!M9 K&#$(L;&8#quot;';$ >-quot;7;&'quot;N*Q)6;&% .)/,/*+0A*>-quot;7;&'quot;')(2*@)-quot;(67)*F)&(;$)$$;&8%#quot;)'* .FS@99 Bernhard Haslhofer, Linked Data Tutorial 140 Friday, March 6, 2009
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. Bernhard Haslhofer, Linked Data Tutorial 141 Friday, March 6, 2009
Demo 1 - browsing and querying DBPedia • http://dbpedia.org/resource/Hallstatt_culture • http://dbpedia.org/snorql • http://lookup.dbpedia.org Bernhard Haslhofer, Linked Data Tutorial 143 Friday, March 6, 2009
Demo 2 - cURLing the LIBRIS catalogue • LIBRIS = The Swedish Union Catalog • Starting point: http://libris.kb.se/bib/10432900 Bernhard Haslhofer, Linked Data Tutorial 144 Friday, March 6, 2009
Demo 3 - exposing MySQL DB using D2R • sample database: http://dev.mysql.com/doc/world- setup/en/world-setup.html Bernhard Haslhofer, Linked Data Tutorial 145 Friday, March 6, 2009
Demo 4 - sample OAI2LOD instances • http://www.mediaspaces.info/tools/oai2lod/ Bernhard Haslhofer, Linked Data Tutorial 146 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 147 Friday, March 6, 2009
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 Bernhard Haslhofer, Linked Data Tutorial 148 Friday, March 6, 2009
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... Bernhard Haslhofer, Linked Data Tutorial 149 Friday, March 6, 2009
Summary Bernhard Haslhofer, Linked Data Tutorial 150 Friday, March 6, 2009
Questions / Discussion Bernhard Haslhofer, Linked Data Tutorial 151 Friday, March 6, 2009

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