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

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

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:sharedContenta:externalContent <http://somewhere/RDF/ont.owl>

N3 RDF example

15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 4

NewcastleCity Council

Pollution data City: Newcastle Country: UK Values: … Units: Measurements: … Compound: …

Linked Open Data

UK government

World HealthOrganisation

Government data City: Newcastle Population: … Lat: … Long: …

Exposure levels Compound: Max Levels: … (more data)

HTTP

HTTP

Data consumer

15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 5

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

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

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

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

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

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

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

consumerTrustedprovider

Trusted?

Trusted?

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)

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

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

Applications

● Open Government● The Web Of Things

– Massive real-time structured sensor data

● The DataHub● Data.gov● PublicData.eu● Association mining● Intelligent recommendation systems

15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 16

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

15/03/2013 Research Skills, MSc ITEC Rui M. Vieira 17

Questions ?

slide:question

en:noun

ens:part

slide:enquiryowl:sameAs

speech:property

rdfs:type