Presentation for 5th International Workshop on Data Engineering meets the Semantic Web (DESWeb) In conjunction with ICDE 2014, Chicago IL, USA, March 31, 2014 held by Kai Schlegel

1. DESWeb 2014
ICDE 2014, Chicago IL, USA, March 3
balloon Fusion
SPARQL Rewriting Based on
Unified Co-Reference Information
Kai Schlegel (kai.schlegel@googlemail.com)
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

4. 4

5. 5

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!
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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.

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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!

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Components
balloon toolsuite

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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

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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

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1. Determine synonym URIs
SELECT ?p ?o WHERE {
<http://de.dbpedia.org/resource/Passau> ?p ?o.
}
SPARQL

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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

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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

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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
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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
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Optimizations (ongoing)

20. balloon Overflight
Results
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Results from a sounding
balloon

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balloon toolsuite

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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)
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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