1. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 1
Linked Open Data
State of the art, challenges and applications
Part of the Linking Open (LOD) Data Project Cloud Diagram

2. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 2
Open Data
● What is Open Data?
– Non-proprietary and standard format
– Machine computable
– Non-discriminatory

3. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 3
What is Linked Open Data
● Open Data Distributed over the network
● Standardised format
– Resource Description Format (RDF) as data model
– SPARQL for queries
● RDF “Triples” serialised as
– XML, N3 or many other standards
● Semantics and Ontologies
● Architecture similar to WWW
– Hypertext Transfer Protocol (HTTP)
– Domain Name System (DNS)
– Uniform Resource Identifiers (URIs)
@prefix a:
<http://example.com/2013/02/A#> .
@prefix b:
<http://example.net/2013/02/B#> .
@prefix eg:
<http://example.com/> .
eg:sharedContent
a:externalContent
<http://somewhere/RDF/ont.owl>
N3 RDF example

4. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 4
Newcastle
City Council
Pollution data
City: Newcastle
Country: UK
Values: …
Units:
Measurements: …
Compound: …
Linked Open Data
UK government
World Health
Organisation
Government data
City: Newcastle
Population: …
Lat: …
Long: …
Exposure levels
Compound:
Max Levels: …
(more data)
HTTP
HTTP
Data consumer

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6. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 6

7. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 7
Issues
● Data quality
– Syntax error, invalid semantics
● Scalability
– Unavailability, unresponsiveness
● Security
– Trust, Encryption
● Currency
– Temporal context, versioning
● Aggregation
– Co-referencing, source

8. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 8
Issues
● Data quality
– Syntax error, invalid semantics
● Scalability
– Unavailability, unresponsiveness
● Security
– Trust, Encryption
● Currency
– Temporal context, versioning
● Aggregation
– Co-referencing, source

9. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 9
Data Quality
● Tim Berners-Lee LOD principles
● Syntactically valid
– Several validators
● RDFAlerts, Vapour
– Frameworks to build own tools
● Redland RDF (C library to build RDF parsers)
– Allow to gather metrics on conformance
● Dataset scoring
validator
Data
metrics

10. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 10
Data Quality
● Semantically valid
– Use standard vocabularies and ontologies when
possible
– Use Domain specific vocabularies:
● eg SensorML for data-in-motion
● Vast amount for medicine, bioinformatics, etc.
● Linked Open Vocabularies database

11. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 11
Scalability
● Unavailable or unresponsive providers
– Non-dereferenceable resources is missing data
– LOD uses HTTP and WS
● HTTP status codes to convey more information
– Redirect to other resources
● Caching
● Dataset dumps
– Use analytics to provide useful information
● Profile servers
● Tune servers
● Plan scalability

12. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 12
Security
● Trust
– Community scoring of datasets and providers
– Provenance
● Watermarking
– All attributes can be in meta-data
● Encrypted channels
– SSL, certificates to ensure provenance
consumer
Trusted
provider
Trusted?
Trusted?

13. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 13
Currency
● Temporal context for data
– Facebook hits/day: average? Specific day?
● Is data versioned?
– Are we mixing old and new data?
● Solutions:
– Currency meta-data
● At the statement level, not just dataset level
– Specific ontologies for current (OntoCurrency)

14. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 14
Aggregation
● Co-reference
– Discovering co-referents
– Resolution of co-referents
● Multiple sources
– Discovery
– SPARQL over remote datasets
● Software solutions
– Semantic Web Client Library
● Handles dereferencing and aggregation
– DARQ
● Multi-source SPARQL queries
example.net example.com
1203 A
P
consumer
Person A?
http://example.com/
People/A
http://example.net/
2013/Staff/1203

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Applications
● Open Government
● The Web Of Things
– Massive real-time structured sensor data
● The DataHub
● Data.gov
● PublicData.eu
● Association mining
● Intelligent recommendation systems

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Conclusion
● LOD is becoming a preferred solution for data providers
● Obstacles to the global, machine computable, linked
Semantic Web
● No integrated solution dealing with all the issues
● But solutions exist
– To deal with specific areas
– To build new tools

17. 15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 17
Questions ?
slide:question
en:noun
ens:part
slide:enquiry
owl:sameAs
speech:property
rdfs:type