With the increased availability of data on the Semantic Web, the question whether data sources offer data of appropriate quality for a given purpose becomes an issue. With CORNER, we specifically address the data quality aspect of completeness. We demonstrate a formal way to state for which topics an RDF source is complete and how to use such statements to automatically analyze whether a given query will return a complete answer over a source. CORNER supports SPARQL BGP queries and can take RDFS ontologies into account in its analysis. If a query can only be answered completely by a combination of sources, CORNER rewrites the original query into one with SPARQL SERVICE calls, which assigns each query part to a suitable source, and executes it over those sources. CORNER builds upon previous work by Darari et al. and is implemented using standard Semantic Web frameworks.

1. CORNER: A Completeness Reasoner for SPARQL Queries
over RDF Data Sources
Fariz Darari
Radityo Eko Prasojo
Werner Nutt
EPCL Workshop 2014, Dresden
Supported by the project MAGIC, funded by the province of Bolzano
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2. Intro
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3. Intro
Completeness
statement about the
IMDB data source
Quentin Tarantino
was the character
Mr. Brown
……………
……………
……………
http://www.imdb.com/title/tt0105236/fullcredits?ref_=tt_ov_st_sm#cast
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4. Intro
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5. Motivations
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6. Motivations
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7. Motivations
Darari et al.1
developed a logical framework for
completeness reasoning techniques on the Semantic Web
The framework enables creation of descriptions as to which
parts of a data source are complete, called completeness
statements
Checks whether a query returns a complete result, called
query completeness checks, are then possible
However, implementation is still missing
1
Fariz Darari, Werner Nutt, Giuseppe Pirró, Simon Razniewski:
Completeness Statements about RDF Data Sources and Their Use for Query
Answering. ISWC 2013
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8. CORNER
We built an implementation of the framework, called
CORNER (short for Completeness Reasoner :)
A Web-based demo can be accessed at
http://corner.inf.unibz.it/
Implementation reused the Apache Jena (Semantic Web
library) and Google Web Toolkit (User Interface library)
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9. CORNER: Functionalities
Users can specify SPARQL basic graph pattern (BGP)
queries, whose completeness is to be checked.
Users can specify completeness statements of a specific
data source. There are also the options to upload and
download completeness statements in CORNER.
Users can specify RDFS ontologies for use in
completeness reasoning.
If a query is analyzed to be complete, CORNER can rewrite
the query into an executable, federated query whose
answers are complete.
From completeness reasoning results, users may see the
debugging information to learn why the query can be
answered completely.
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10. CORNER: Screenshot
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11. CORNER: Architecture
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12. CORNER: Reasoning Steps
From the query Q, CORNER generates an initial graph Gi
Q
representing the information needed for answering the
query
Every completeness statement C is translated into a
SPARQL CONSTRUCT query QC
Application of all the queries QC to the graph Gi
Q results in a
subgraph Ga
Q of Gi
Q, representing parts of the query for
which data are complete
By evaluating Q over Ga
Q, CORNER tests whether the
complete data are sufficient to answer Q
If Q can be answered completely, based on the data
sources information of the completeness statements that
contribute to generate Ga
Q, CORNER distributes the query
parts of Q to their suitable, complete sources
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13. CORNER: Demo
Link to Demo Video on Youtube
http://bit.ly/cornerDemo
Link to CORNER
http://corner.inf.unibz.it/
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