Ghislain Atemezing, Bernard Vatant, Raphaël Troncy, Pierre-Yves Vanderbussche

Harmonizing services for LOD vocabularies: a case study

Goal and Agenda

§  Goal: align services against Linked Open Vocabularies to harmonize and manage vocabularies’ namespaces

§  Motivation Ø  Identify vocabularies using namespace Ø Catalogs of vocabularies

§  Services managing vocabularies Ø Prefix.cc versus LOV Ø Different policies but same goal

§  Aligning LOV with Prefix.cc

§  Towards governance of vocabularies

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Prefixes lookup headache

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What <wo> namespace stands for? PREFIX.CC

LOV

QNames and vocabulary namespaces

§  Usage of namespaces Ø From XML syntax with xmlns declarations Ø Use to identify a valid namespace

§  On the Semantic Web Ø Extended notion of namespace for other RDF

serialization (N3, Turtle) Ø Some de facto prefixes emerging: rdfs:, foaf:, rdf: owl: Ø SPARQL endpoints use a list of built-in prefixes not

transparent to the developers

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Why if … global use of prefixes

§  Global namespaces Ø With good practices to

recommend a prefix Ø Have a more transparent

list of built-in prefixes Ø All the services

understand each other with prefixes

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Accessing vocabularies

§  Catalogs of vocabularies Ø Hosting vocabularies with search, review or download

features Ø Curated manually or semi-automatically

§  Services Ø Help finding vocabularies or detect namespaces Ø Look up services: Prefix.cc, vocab.cc Ø Triple-Checker, YASGUI

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Existing catalogs of vocabularies

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Many overlapped of vocabularies among different catalogs

LOV in a Nutshell : http://lov.okfn.org/dataset/lov/

§  A curated list of vocabularies Ø More than 360 vocabularies Ø Each of them described by vocabulary-of-a-friend

(voaf) Ø Provide a dump in .n3 of the different versions of a

vocabulary

§  Some related services Ø SPARQL endpoint: http://lov.okfn.org/endpoint/lov Ø Search function: http://lov.okfn.org/dataset/lov/search Ø An Aggregator endpoint: http://lov.okfn.org/endpoint/lov_aggregator Ø An intelligent bot agent for updates:

http://lov.okfn.org/dataset/lov/bot

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LOV DESCRIPTION

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CORE FEATURES OF THE FRAMEWORK  

Domain   Intended Use   Collection   Gatekeeping  Number of Ontologies   Dynamics  

Search metadata  

Search within

ontology  

Search across ontologies  

Navigation criteria  

General  

Promote and facilitate the reuse of vocabularies in the linked data ecosystem.  

Submitted by any user via LOV-Suggest tool.  

Manual curation and

automatic URI validation  

370   Growing  Yes, with

visual depiction  

Yes  

Keyword-based; structured

search (query-based)  

Ordered by prefix,

namespace, title and

visual links navigation  

CORE FEATURES OF THE FRAMEWORK  

Metrics   Comments and review  

Ranking  Web

service access  

SPARQL endpoint  

Content available  

Read/Write  

Ontology directory  

Ontology registry  

Application platform  

 

Reuse popularity on

the LOD Cloud  

N/A - Only by the curators  

Metric-based   API   Yes  

Ontology metadata

, URI  Read   Yes   Yes   Yes    

LOV DESCRIPTION WITH THE FRAMEWORK OF [d’Aquin-Noy2012-Survey]

Prefix.cc in a Nutshell: http://prefix.cc

§  A service to look up vocabularies Ø More than 1200 namespaces registered Ø Anyone can add prefixes Ø In case of conflicts, users can vote

§  Some related services Ø Namespace lookup API: http://prefix.cc/about/api Ø Reverse lookup API: http://prefix.cc/reverse

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LOV versus PREFIX.CC

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Continuously growth of namespaces registered in prefix.cc. Clearly view of the results of the harmonization process started in March, 2013

Aligning LOV with Prefix.cc (1)

§  Scenarios Ø Conflicts between prefix.cc and LOV Ø Prefixes in LOV not present in prefix.cc Ø URIs in prefix.cc that are actually LOV-able

vocabularies

§  Method Ø Federated query in SPARQL 1.1 Ø Jena ARQ command line

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Aligning LOV with Prefix.cc (2)

§  Dealing with conflicts Ø Clashes: same prefix but different URIs Ø Disagreements on preferred namespace

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§  Actions in case of disagreement Ø Generally 4 types of actions Ø  Important: social aspect to contact the editors of the

vocabularies

Vocabularies leading to contact editors

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§  Contacting editors/maintainers Ø Via social platforms: LinkedIn, Google+, Twitter, email Ø Data retrieved mainly from vocabulary metadata.

Finding Vocabularies in Prefix.cc

§  LOV check API: http://lov.okfn.org/dataset/lov/apidoc/ Ø Find out namespaces in Prefix.cc that are vocabularies Ø Extract them as candidate vocabularies for LOV

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Some Results

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Category Number

lov-­‐able  vocabs   227  Intersect-­‐prefixes   188  vocabs  in  LOV   321  vocabs  in  prefix.cc   925  

14%  

11%  

19%  56%  

Findings  during  alignment  process  

lov-­‐able  vocabs  

Intersect-­‐prefixes  

vocabs  in  LOV  

vocabs  in  prefix.cc  

More than 200 prefixes are vocabularies

Conclusion and Future Work

§  We have presented a way to manage prefixes Ø By analyzing vocabularies in LOV and prefix.cc Ø By providing mechanism of aligning two services dealing

with vocabulary prefixes

§  Future work Ø Provide a unique interface for submission of namespaces

and prefixes to both services Ø Publish a list of common recommended prefixes Ø Foster and support current effort towards a more

sustainable governance of vocabularies.

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Q/A Session

Thanks for your attention!