Introduction to SPARQL

Andrea Nuzzolese nuzzoles@cs.unibo.it

Bologna, 28 Marzo 2011

Laurea Magistrale in Scienze di Internet KMDM a.a. 2010/2011

SPARQL

• SPARQL (pronounced "sparkle”) is an RDF query language

• it stands for Simple Protocol And RDF Query Language

• allows for a query to consist of triple patterns, conjunctions, disjunctions, and optional patterns

Anatomy of a QueryPREFIX foo: <…>PREFIX bar: <…>…SELECT …FROM <…>FROM NAMED <…>WHERE { …}GROUP BY …HAVING …ORDER BY …LIMIT …OFFSET …BINDINGS …

Declare prefixshortcuts (optional)

Query result clause

Query pattern

Query modifiers(optional)

Define the dataset (optional)

courtesy of Lee Feigenbaum

Types of SPARQL QueriesProject out specific variables and expressions:

SELECT ?c ?cap (1000 * ?people AS ?pop)

Project out all variables:SELECT *

Project out distinct combinations only:SELECT DISTINCT ?country

Results in a table of values (in XML or JSON):

SELECT queries

?c ?cap ?pop

ex:France ex:Paris 63,500,000

ex:Canada ex:Ottawa 32,900,000

ex:Italy ex:Rome 58,900,000

Construct RDF triples/graphs:CONSTRUCT { ?country a ex:HolidayDestination ; ex:arrive_at ?capital ; ex:population ?population .}

Results in RDF triples (in any RDF serialization):

ex:France a ex:HolidayDestination ; ex:arrive_at ex:Paris ; ex:population 635000000 .ex:Canada a ex:HolidayDestination ; ex:arrive_at ex:Ottawa ; ex:population 329000000 .

CONSTRUCT queries

Ask whether or not there are any matches:ASK

Result is either “true” or “false” (in XML or JSON):true, false

ASK queriesDescribe the resources matched by the given

variables:DESCRIBE ?country

Result is RDF triples (in any RDF serialization) :ex:France a geo:Country ; ex:continent geo:Europe ; ex:flag <http://…/flag-france.png> ; …

DESCRIBE queries

courtesy of Lee Feigenbaum

Nuts & Bolts

Write full URIs:<http://this.is.a/full/URI/written#out>

Abbreviate URIs with prefixes:PREFIX foo: <http://this.is.a/URI/prefix#>… foo:bar …

http://this.is.a/URI/prefix#bar

Shortcuts:a rdf:type

URIsPlain literals:

“a plain literal”

Plain literal with language tag:“bonjour”@fr

Typed literal:“13”^^xsd:integer

Shortcuts:true “true”^^xsd:boolean3 “3”^^xsd:integer 4.2 “4.2”^^xsd:decimal

Literals

Variables:?var1, ?anotherVar, ?and_one_more

VariablesComments:

# Comments start with a ‘#’# continue to the end of the line

Comments

Match an exact RDF triple:ex:myWidget ex:partNumber “XY24Z1” .

Match one variable:?person foaf:name “Lee Feigenbaum” .

Match multiple variables:conf:SemTech2009 ?property ?value .

Triple Patterns

courtesy of Lee Feigenbaum

Some Public SPARQL EndpointsName URL What’s there?

SPARQLer http://sparql.org/sparql.htmlGeneral-purpose query endpoint for Web-accessible data

DBPedia http://dbpedia.org/sparqlExtensive RDF data from Wikipedia

DBLP http://www4.wiwiss.fu-berlin.de/dblp/snorql/Bibliographic data from computer science journals and conferences

LinkedMDB

http://data.linkedmdb.org/sparqlFilms, actors, directors, writers, producers, etc.

WorldFactbook

http://www4.wiwiss.fu-berlin.de/factbook/snorql/

Country statistics from the CIA World Factbook

bio2rdf http://bio2rdf.org/sparqlBioinformatics data from around 40 public databases

SPARQL Over HTTP (the SPARQL Protocol)http://host.domain.com/sparql/endpoint?<parameters>

where <parameters> can include:

query=<encoded query string>

e.g. SELECT+*%0DWHERE+{…default-graph-uri=<encoded graph URI>

e.g. http%3A%2F%2Fexmaple.com%2Ffoo…n.b. zero of more occurrences of default-

graph-urinamed-graph-uri=<encoded graph URI>

e.g. http%3A%2F%2Fexmaple.com%2Fbar…n.b. zero of more occurrences of named-graph-

uri

HTTP GET or POST. Graphs given in the protocol override graphs given in the query.

SPARQL Resources

• The SPARQL Specification– http://www.w3.org/TR/rdf-sparql-query/

• SPARQL implementations– http://esw.w3.org/topic/SparqlImplementations

• SPARQL endpoints– http://esw.w3.org/topic/SparqlEndpoints

• SPARQL Frequently Asked Questions– http://www.thefigtrees.net/lee/sw/sparql-faq

• SPARQL Working Group– http://www.w3.org/2009/sparql/wiki/

• Common SPARQL extensions– http://esw.w3.org/topic/SPARQL/Extensions

Semantic Web Frameworks

Andrea Nuzzolese nuzzoles@cs.unibo.it

Bologna, 28 Marzo 2011

Laurea Magistrale in Scienze di Internet KMDM a.a. 2010/2011

Overview

OWL API

• It implements the OWL2 Model• it handles OWL model in Java

• It implements the RDF Model• It also offers API for OWL• It provides a SPARQL implementation called ARQ

• Semantic lifting of text• Knowledge representation• Reasoning• RDF refactoring• Triplification• RDF storage

What is Jena?• open-source Java implementation of core Semantic Web

- RDF graph manipulation API- RDFS and OWL reasoning API- Includes the de facto reference RDF/XML parser- RDF/XML, N3 and N-triple Input/Output- SPARQL query engine- rule-based inference engine

• in-memory or persistent storage- Jena TDB- Jena SDB

• developed by HP Laboratories

• now an Apache Incubator project

Key concepts

• the Jena API builds on RDF

• core API classes are– Model: the representation of an RDF model and is

composed by a set of statements– Statement: is a triple subject-object-predicate

• the subject is a resource• the predicate is a property• the object is a value or a resource

– Resource: an object identified by an URI– Property: a particular resource that describes relations

between resources

Creating a RDF graph

• we use Jena to create a new RDF graph, with a triple which states that– Sir Tim Berners-Lee is a person and his name

is “Tim Berners-Lee”

http://…/Berners-Leefoaf:Personrfd:type Tim

Berners-Lee

foaf:name

RDF API// basic definitionsString uri = "http://www.w3.org/People/Berners-Lee";String fullName = "Tim Berners-Lee";

// create an empty (default) model via ModelFactoryModel model = ModelFactory.createDefaultModel();

// create the resource that identifies Tim Berners-Lee as a personResource timBernersLee = model.createResource(uri,

FOAF.Person);

// add the name property to the resource identifying TBLtimBernersLee.addProperty(FOAF.name, fullName);

http://…/Berners-Leefoaf:Personrfd:type Tim

Berners-Lee

foaf:name

Jena I/O//we want to fetch the RDF graph of Tim Berners-Lee from DBpediaString tblURI = "http://dbpedia.org/resource/Tim_Berners-Lee";

//we load the RDF into a Jena ModelModel model = FileManager.get().loadModel(tblURI, "RDF/XML");

//we print the RDF to standard inputmodel.write(System.out);

//we save the RDF into a local filetry {

OutputStream os = new FileOutputStream(new File("out/tbl.n3"));model.write(os, "N3");

} catch (FileNotFoundException e) {e.printStackTrace();

}

SPARQL APIModel model = …;

// define the SPARQL query stringString queryString = "SELECT ?person ?name WHERE {" +

"?person <http://xmlns.com/foaf/0.1/name> ?name" + "}";

// create the query for JenaQuery query = QueryFactory.create(queryString);QueryExecution qExec = QueryExecutionFactory.create(query, model);

// execute the queryResultSet rs = qExec.execSelect();

while(rs.hasNext()){QuerySolution qSolution = rs.next();

// get the person and the nameResource person = qSolution.getResource("person");Literal name = qSolution.getLiteral("name");

System.out.println(person.getURI() + " has name " + name.getString());}

Storage and named graphs

// basic definitionsString bernersLeeName = "http://foo/Berners-Lee";String stebeJobsName = "http://foo/SteveJobs";

// create models named http://foo/Berners-Lee and http://foo/SteveJobs respectivelyModel bernersLeeModel = TDBFactory.createNamedModel(bernersLeeName,

"tmp/storage");Model steveJobsModel = TDBFactory.createNamedModel(stebeJobsName,

"tmp/storage");

// get the reference to the union graph of the graphs into the triple storeModel unionModel = TDBFactory.createNamedModel("urn:x-arq:UnionGraph",

"tmp/storage");

What is the OWL API?

• a Java framework for OWL2• a reference implementation for creating,

manipulating and serializing OWL Ontologies

• is open source and is available under the LGPL License

• provides an implementation of SWRL• is open to reasoners

OWL API

Key concepts

• OWL API completely builds on OWL2• the root object is the OWLOntologyManager,

that manages in-memory a set of OWL ontologies

• an OWLOntology is a set of OWL axioms• an OWLAxiom is a proposition that is not

proved but considered to be self-evident

OWL API

Adding OWL axioms// create the IRI for the ontologyString iriString = "http://foo/myontology";IRI ontologyIRI = IRI.create(iriString);

// create the ontology managerOWLOntologyManager manager = OWLManager.createOWLOntologyManager();

// create the ontology identified the ontologyIRI OWLOntology ontology = manager.createOntology(ontologyIRI);

// get the factory that allows to specify axiomsOWLDataFactory factory = manager.getOWLDataFactory();

OWLClass clsA = factory.getOWLClass(IRI.create(iriString+ "#A"));OWLClass clsB = factory.getOWLClass(IRI.create(iriString+ "#B"));

// create the axiomOWLAxiom axiom = factory.getOWLSubClassOfAxiom(clsA, clsB);

// add the axiom to the ontologyAddAxiom addAxiom = new AddAxiom(ontology, axiom);

// apply the change using the managermanager.applyChange(addAxiom);

OWL API

Reasoning// get the simple configuration for the reasonerOWLReasonerConfiguration config = new SimpleConfiguration();

// we need a concrete reasoner.// here there is a dependency with HermiT ReasonerFactory risfactory = new ReasonerFactory(); // create the reasonerOWLReasoner reasoner = risfactory.createReasoner(ontology,config); // ask the reasoner to do all the necessary work nowreasoner.precomputeInferences(); // ask if the ontology is consistentboolean consistent = reasoner.isConsistent(); if(consistent){ NodeSet<OWLClass> subClses = reasoner.getSubClasses(clsA, true);}else{ Node<OWLClass> bottomNode = reasoner.getUnsatisfiableClasses();}

OWL API

References

• http://owlapi.sourceforge.net/index.html

• Matthew Horridge, Sean Bechhofer.

The OWL API: A Java API for Working with OWL 2 Ontologies. OWLED 2009, 6th OWL Experienced and Directions Workshop, Chantilly, Virginia, October 2009.– http://www.webont.org/owled/2009/papers/

owled2009_submission_29.pdf

OWL API

What is Stanbol?• modular software stack • reusable set of components for semantic content

management• it offers:

- semantic lifting (Enhancer)- knowledge representation (OntoNet)- reasoning (Reasoner)- refactoring (Refactor)- triplification (Reengineer)- caching of entities from Linded Data (EntityHub)- storage of RDF (Store)

• Apache Incubator project• IKS project

The IKS stack

Semantic lifting (Enhancer)

• it implements a simple OSGi-based RESTful engine

• it enhances textual content, using pluggable enhancement engines– named entity recognition– Linked Data entity matching (DBPedia and

GeoNames)

KReS

Ontology Network

EntityHub

References

• the IKS wiki– http://wiki.iks-project.eu/index.php/Main_Page

• the Apache Stanbol home – http://incubator.apache.org/stanbol/index.html

• the source code– http://svn.apache.org/repos/asf/incubator/

stanbol/trunk/