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Day 2 RISIS Linked Data Course Overview of the Course: Friday 9:00-9:15 Coffee 9:15-9:45 Introduction & Reflection 10:30-11:30 SPARQL Query Language 11:30-11:45 Coffee 11:45-12:30 SPARQL Hands-on 12:30-13:30 Lunch 13:30-14:00 Linksets & Lenses for Aligning Datasets 14:00-14:30 Linked Data Publishing 14:30-14:45 Coffee 14:45-16:00 Data Publishing Hands-On 16:00-17:00 Actual Research SPARQL Query Language Rinke Hoekstra, [email protected] Questions Goals • How can we query Linked Data • Know the syntax of SPARQL • What is the syntax of SPARQL • Understand how to query Linked Data on the Web • How can we use SPARQL • Know about standard vocabularies in Linked Data Deep Breath by Tomas A RDF - Where is it? • As separate files, e.g. as .ttl, .rdf, .nt, etc. • Integrated with Web pages (RDFa/Microdata) • Accessible through content negotiation curl -L -H "Accept: text/turtle" "http://dbpedia.org/resource/Inside_Out_(2015_film)" curl -L -H "Accept: text/html" "http://dbpedia.org/resource/Inside_Out_(2015_film)" • In RDF-specific databases called triple stores • A standard HTTP REST API for querying using the SPARQL language • This API is called a SPARQL endpoint SPARQL - The SPARQL Protocol and RDF Query Language • The SPARQL Protocol specifies how to query Triple stores over HTTP • The SPARQL Query Language specifies a syntax for writing queries • There are six types of queries SELECT, CONSTRUCT, INSERT, DELETE, ASK, DESCRIBE ? http://www.w3.org/TR/sparql11-query SPARQL - Query Syntax PREFIX: the namespace prefixes used in the SPARQL query PREFIX dbo: <http://dbpedia.org/ontology/> SELECT ?city WHERE { ?city dbo:areaCode "020". } LIMIT 10 SELECT: the entities (variables) you want to return WHERE: the (sub)graph you want to get information from ... including additional constraints on results (using operators) http://www.w3.org/TR/sparql11-query SPARQL - Graph Pattern • The WHERE clause specifies a graph pattern • … that should be matched • … can match multiple times • A graph pattern is an RDF graph with some nodes & edges as variables dbo:Country "020"^^xsd:string rdf:type ? ? dbo:capital ? SPARQL - Triple Patterns • A graph pattern consists of multiple triple patterns • A triple pattern is a triple with zero or more variables ?x dbo:capital dbpedia:Amsterdam . ?x dbo:capital ?y . ?x dbo:areaCode "020". ?x ?p ?y dbo:Country "020"^^xsd:string dbpedia:Netherlands rdf:type dbo:Country ; rdf:type dbo:capital dbpedia:Amsterdam . dbpedia:Amsterdam dbo:areaCode "020"dbo:areaCode. dbpedia:The_Netherlands dbo:capital dbpedia:Amsterdam SPARQL - Triple patterns form a conjunction Every triple pattern should match PREFIX dbo: <http://dbpedia.org/ontology/> dbo:Country "020"^^xsd:string SELECT ?x WHERE { ?x dbo:capital ?y . rdf:type ? ?y dbo:areaCode "020". } LIMIT 10 ? dbo:capital ? dbo:Country "020"^^xsd:string "020"^^xsd:string rdf:type dbo:areaCode dbo:areaCode dbpedia:The_Netherlands dbo:capital dbpedia:Amsterdam dbpedia:Westminster http://www.w3.org/TR/sparql11-query ✖ SPARQL - But we can also use disjunctions At least one of the graph patterns should match PREFIX dbo: <http://dbpedia.org/ontology/> SELECT ?y WHERE { { ?y dbo:areaCode "020". } UNION { ?y dbo:areaCode "010". } } LIMIT 10 "020"^^xsd:string "010"^^xsd:string dbo:areaCode dbo:areaCode dbpedia:Amsterdam dbpedia:Rotterdam http://www.w3.org/TR/sparql11-query SPARQL - Optional graphs A part of the graph pattern is optional, and does not need to match PREFIX dbo: <http://dbpedia.org/ontology/> SELECT ?x ?y WHERE { ?y dbo:areaCode "020". OPTIONAL { ?x dbo:capital ?y . } } LIMIT 10 dbo:Country "020"^^xsd:string "020"^^xsd:string rdf:type dbo:areaCode & dbo:areaCode dbpedia:The_Netherlands dbo:capital dbpedia:Amsterdam dbpedia:Westminster http://www.w3.org/TR/sparql11-query Filtering query results Tests in the FILTER clause have to be validated for matching subgraphs PREFIX dbo: <http://dbpedia.org/ontology/> SELECT ?y WHERE { ?y dbo:areaCode "020". ?y dbo:populationTotal ?x . FILTER (?x > 500000) } "020"^^xsd:string dbo:areaCode "790654"^^xsd:integer dbpedia:Amsterdam dbo:populationTotal "020"^^xsd:string dbo:areaCode http://www.w3.org/TR/sparql11-query dbpedia:Borehamwood ✖dbo:populationTotal "28546"^^xsd:integer SPARQL - Solution modifiers Sorting using ORDER BY PREFIX dbo: <http://dbpedia.org/ontology/> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> DISTINCT results SELECT ?label WHERE { ?place dbo:areaCode "020"; rdfs:label ?label . PREFIX dbo: <http://dbpedia.org/ontology/> PREFIX dbpedia: <http://dbpedia.org/resource/> } ORDER BY DESC (?label) PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT DISTINCT ?name WHERE { ?country rdf:type dbo:Country ; dbo:capital ?ams . LIMITing the number of results ?ams dbo:country dbpedia:Netherlands ; rdfs:label ?name . FILTER (lang(?name) = "en" ) PREFIX dbo: <http://dbpedia.org/ontology/> } PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> SELECT ?label WHERE { ?y dbo:areaCode "020"; rdfs:label ?label . FILTER (lang(?label) = "en" ) } ORDER BY DESC(?label) LIMIT 10 SPARQL - Property Paths • Not interested in variable bindings • Transitively walk over the same property relation • Are interested in alternatives without having to write a UNION PREFIX dbo: <http://dbpedia.org/ontology/> PREFIX dbpedia: <http://dbpedia.org/resource/> PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX skos: <http://www.w3.org/2004/02/skos/core#> SELECT DISTINCT ?name WHERE { ?country rdf:type dbo:Country ; dbo:capitalPREFIX dbo: ?city<http://dbpedia.org/ontology . /> { ?city rdfs:labelPREFIX dbpedia: ?name <http://dbpedia.org/resource/ . } > UNION PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> { ?city skos:prefLabelPREFIX skos: ?name<http://www.w3.org/2004/02/skos/core#> . } FILTER (lang(?name ) = "en" ) } SELECT DISTINCT ?name WHERE { ?country rdf:type dbo:Country ; dbo:capital/(rdfs:label|skos:prefLabel) ?name . } FILTER (lang(?name) = "en" ) } PREFIX dbo: <http://dbpedia.org/ontology/> PREFIX ex: <http://example.com/vocab/> • SELECT returns a table with CONSTRUCT { variable bindings ?y ex:kengetal "020". } WHERE { ?y dbo:areaCode "020". } • CONSTRUCT returns a RDF graph PREFIX dbo: <http://dbpedia.org/ontology/> PREFIX dbr: <http://dbpedia.org/resource/> • ASK returns true or false ASK WHERE { dbr:Amsterdam dbo:areaCode "020". } • DESCRIBE returns a RDF graph PREFIX dbr: <http://dbpedia.org/resource/> • INSERT is like CONSTRUCT, DESCRIBE dbr:Amsterdam but inserts the graph into the triple store PREFIX dbo: <http://dbpedia.org/ontology/> PREFIX ex: <http://example.com/vocab/> INSERT { ?y ex:kengetal "020". } WHERE { ?y dbo:areaCode "020". } http://www.w3.org/TR/sparql11-query SPARQL Update SPARQL - More features • Named Graphs • Negation provide context for statements they contain MINUS GRAPH <http://example.com> { … } • Functions • Aggregates IF, BOUND, EXISTS, NOT EXISTS, IN, NOT IN COUNT, SUM, MIN, MAX, AVG, GROUP_CONCAT &&, ||, =, <, >, =>, =< isIRI, isBlank, isLiteral, isNumeric, str, and SAMPLE lang, datatype STRLEN, SUBSTR, CONTAINS, CONCAT, REGEX now, year, month, day, hours, minutes, • Grouping and group aggregates seconds GROUP BY and HAVING … and more • Provide data inline VALUES http://www.w3.org/TR/sparql11-query http://yasgui.org SPARQL - Querying the Linked Data Cloud + = • DBPedia • LOD Cache: DBPedia + Geonames + NY Times + MusicBrainz + ... PREFIX dbo: <http://dbpedia.org/ontology/> PREFIX owl: <http://www.w3.org/2002/07/owl#> SELECT DISTINCT ?x ?y WHERE { ?x dbo:areaCode "020". ?y owl:sameAs ?x . FILTER (?x != ?y) } • Same query, different results! SPARQL - Summary • Linked Data is usually stored in triple stores • SPARQL is the query language for the Web of Linked Data • Queries are sent to SPARQL endpoints over HTTP • Queries describe graph patterns with variables • Graph patterns match (parts of) the RDF graphs stored in the triple store • Results are returned as a table with variable bindings (JSON, XML, TSV, CSV…) LinkedLinked Data Open LifecycleData Interlinking Authoring Enrichment Linked (Open) Data Storage/ Quality Querying Lifecycle Analysis Extraction Evolution Exploration http://stack.linkeddata.org/ Ali Khalili Designing Linked Data Applications 14 Exploration Exploration RDF - Vocabularies • The RDF vocabulary and RDFS • Geonames reserved terms needed for the data model locations • Friend of a Friend (FOAF) • Data Cube (QB) persons and relations between persons statistical data • Dublin Core (DC and DCTerms) • Simple Knowledge Organization bibliographic attributes (author, title, etc.) System (SKOS) concept hierarchies and mappings • DBPedia Ontology DBPedia is at the heart of the Web of Data • Web Ontology Language (OWL) formal constraints on class membership Exploration RDF - The RDF Vocabulary Namespace <http://www.w3.org/1999/02/22-rdf-syntax-ns#> Usual prefix rdf (NB: needs to be declared, like all others) Important elements rdf:type … links a resource to a type rdf:Resource … is the type of all resources rdf:Property … is the type of all predicates Examples geo:Amsterdam rdf:type rdf:Resource . geo:containedIn a rdf:Property . rdf:type a rdf:Property . Exploration RDFS - The RDF Schema Vocabulary Namespace <http://www.w3.org/2000/01/rdf-schema#> Usual prefix rdfs (NB: needs to be declared, like all others) Important elements rdfs:label … links a resource to its name rdfs:Class … is the type of all “types” rdfs:subClassOf … inheritance over types rdfs:subPropertyOf … inheritance over properties Examples geo:Amsterdam rdfs:label “Amsterdam”@nl . geo:containedIn rdfs:subPropertyOf
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  • SPARQL Query Processing with Conventional Relational Database Systems

    SPARQL Query Processing with Conventional Relational Database Systems

    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by e-Prints Soton SPARQL query processing with conventional relational database systems Steve Harris IAM, University of Southampton, UK [email protected] Abstract. This paper describes an evolution of the 3store RDF storage system, extended to provide a SPARQL query interface and informed by lessons learned in the area of scalable RDF storage. 1 Introduction The previous versions of the 3store [1] RDF triplestore were optimised to pro- vide RDQL [2] (and to a lesser extent OKBC [3]) query services, and had no efficient internal representation of the language and datatype extensions from RDF 2004 [4]. This revision of the 3store software adds support for the SPARQL [5] query language, RDF datatype and language support. Some of the representation choices made in the implementation of the previous versions of 3store made efficient support for SPARQL queries difficult. Therefore, a new underlying rep- resentation for the RDF statements was required, as well as a new query en- gine capable of supporting the additional features of SPARQL over RDQL and OKBC. 2 Related Work The SPARQL query language is still at an early stage of standardisation, but there are already other implementations. 2.1 Federate Federate [6] is a relational database gateway, which maps RDF queries to existing database structures. Its goal is for compatibility with existing relational database systems, rather than as a native RDF storage and querying engine. However, it shares the approach of pushing as much processing down into the database engine as possible, though the algorithms employed are necessarily different.