balloon Fusion: SPARQL Rewriting Based on Unified Co-Reference Information
- 1. DESWeb 2014 ICDE 2014, Chicago IL, USA, March 3 balloon Fusion SPARQL Rewriting Based on Unified Co-Reference Information Kai Schlegel ([email protected]) Florian Stegmaier, Sebastian Bayerl, Michael Granitzer, Harald Kosch
- 2. 2 Motivation SPARQL Rewriting & Federation Intermediate Results Outline supported by the European Commission under the Seventh Framework Program
- 3. 3 Linked Data is the heart of Semantic Web “ - W3C Semantic Web Group
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- 6. • Easy access to Linked Data • Query Linked Open Data with SPARQL • Plethora of tools available • Problems: • Business oriented • Complex setup • Maintenance • „Paper-only“ • Not developer friendly • Simple and „instant“ SPARQL Query Federation (-as-a-Service) 6 Motivation Nothing-as-a-Service
- 7. • How to get information about the German City „Passau“? • Problem: LOD is not a single database! 7 Querying LOD SPARQL SPARQL RDF RDFRDF SELECT ?p ?o WHERE { <http://de.dbpedia.org/resource/Passau> ?p ?o. } de.dbpedia.org Relations, Coordinates, Leader, etc. What about the population? SPARQL
- 8. • Problem: Selection of appropriate endpoints • Send query to some endpoints and aggregate the results? 8 Distributed Querying! SPARQL SPARQL RDF RDFRDF SELECT ?p ?o WHERE { <http://de.dbpedia.org/resource/Passau> ?p ?o. } de.dbpedia.org SPARQL linkedgeodata.org
- 9. • Problem: Different identifier for the same semantic concept 9 Misunderstanding: Co-Referencing SPARQL SPARQL RDF RDFRDF SELECT ?p ?o WHERE { <http://de.dbpedia.org/resource/Passau> ?p ?o. } de.dbpedia.org SPARQL linkedgeodata.org Known problem in linguistic: It’s a spud!“ What?“ I mean potato!“ Co-Referencing: Multiple expressions refer to the same thing.
- 10. 10 Problem = Solution? SPARQL-based crawling of co-reference information Exploit co-reference information for • accomplishing immediate SPARQL rewriting • performing endpoint selection • execute automatic query federation Basic idea: Focusing distributed co-reference information Main principle: Semantic entites over identifier!
- 12. 12 balloon Overflight • SPARQL based crawling of LOD endpoints • Query: Ask for subjects and objects which are related with special predicate • Simplified global view on • Equivalence: owl:SameAs, skos:exactMatch, coref:coreferenceData, ... • Graph-Database Neo4j • Equivalence Cluster: Multiple synonym URIs representing the same semantic entity including Provenance
- 13. 13 balloon Fusion SPARQL Federation setup using co-reference information SPARQL Transformation for each BGP 1. Determine synonym URIs 2. Select suitable endpoints 3. Adapt sub-queries to endpoints 4. Federated querying SELECT ?p ?o WHERE { <http://de.dbpedia.org/resource/Passau> ?p ?o. } SPARQL
- 14. 14 1. Determine synonym URIs SELECT ?p ?o WHERE { <http://de.dbpedia.org/resource/Passau> ?p ?o. } SPARQL
- 15. 15 2. Select suitable endpoints • Provenance based selection (PBS) • Endpoints which are involved in cluster composition • Namespace based selection (NBS) • Prefix and Namespace matching of synonym URLs Summarized: origin of co-reference information and origin of synonym URIs
- 16. 16 2. Select suitable endpoints (2) Assumption: • Provenance information only contains „linkedgeodata.org“ as co-reference origin • Namespaces for freebase and dbpedia available (datahub.io) PBS: Linked-Geo-Data Endpoint NBS: DBPedia endpoint NBS: Freebase endpoint
- 17. 17 3. Adapt sub-queries to endpoints PBS: Linked-Geo-Data Endpoint NBS: DBPedia endpoint NBS: Freebase endpoint SELECT ?p ?o WHERE { <http://rdf.freebase.com/ ns/m.01h5td> ?p ?o. } SPARQL SELECT ?p ?o WHERE { <http://de.dbpedia.org/resource/Passau> ?p ?o. } SPARQL SELECT ?p ?o WHERE { { <http://rdf.freebase.com/ns/m.01h5td> ?p ?o. } UNION { <http://linkedgeodata.org/triplify/node240057351> ?p ?o. } UNION { <http://de.dbpedia.org/resource/Passau> ?p ?o. } } SPARQL SELECT ?p ?o WHERE { <http://de.dbpedia.org/resource/Passau> ?p ?o. } SPARQL
- 18. • W3C SPARQL 1.1 Federated Query Extension (SERVICE) • (Partial) Query can be executed against a remote SPARQL endpoint • Distributed sub-queries don‘t contain SPARQL 1.1 features 18 4. Federated Querying SPARQL SELECT ?p ?o WHERE { SERVICE <http://dbpedia.org/sparql> { <http://de.dbpedia.org/resource/Passau> ?p ?o. } UNION { SERVICE <http://www.freebase.com/base/sparql> { <http://rdf.freebase.com/ns/m.01h5td> ?p ? } } UNION { SERVICE <http://linkedgeodata.org/sparql/> { { <http://rdf.freebase.com/ns/m.01h5td> ?p ?o. } UNION { <http://linkedgeodata.org/triplify/node240057351> ?p ?o. } UNION { <http://de.dbpedia.org/resource/Passau> ?p ?o. } }}}
- 19. • Endpoint status check • Check routine in terms of availability and latency • Minimize sub-queries • Group sub-queries with common endpoint • Push join to endpoint • SPARQL Features • Condense PBS UNION-construct of synonym URIs • SPARQL 1.1 VALUES or FILTER with IN operator • Not well implemented in Linked Data endpoints 19 Optimizations (ongoing)
- 21. 21 Results from a sounding balloon
- 23. 23 Statistics • Datahub.io: Linked Open Data Cloud catalog • 337 datasets in total • 237 expose a SPARQL endpoint • 112 successfully queried for co-reference information • Balloon Dataset (first run) • 17.6M co-reference statements • 22.4M distinct URLs • 8.4M equivalence cluster (~ 2.68 identifier per cluster) • Pending Analysis • Distribution of cluster sizes, Number of different Hosts per cluster • Main representative per cluster & False-Friends
- 24. Open Source: • Demo, information and sources available (MIT License) • X as a Service • SPARQL Rewriting (HTTP API) • Query Federation (SPARQL) 24 http://schlegel.github.io/balloon
- 25. Summary: • SPARQL-based crawling of distributed co-reference information • Exploit co-reference information for SPARQL federation 25 Single Point of Access
- 26. Any questions? “ 26 Research is formalized curiosity. It is poking and prying with a purpose. - Zora Neale Hurston