Semantic Web and Linked Data for cultural heritage materials - Approaches in Europeana
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Semantic Web and Linked Data for cultural heritage materials - Approaches in Europeana

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Presented at DANS Workshop on Linked Data

Presented at DANS Workshop on Linked Data

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Semantic Web and Linked Data for cultural heritage materials - Approaches in Europeana Semantic Web and Linked Data for cultural heritage materials - Approaches in Europeana Presentation Transcript

  • Semantic Web and Linked Data for cultural heritage materials Approaches in Europeana Antoine Isaac Vrije Universiteit Amsterdam Europeana DANS Linked Data and RDF workshop, Den Haag, July 28 th 2010
  • A web of cultural heritage data? ?
    • ?
  • The current portal
  •  
  • Towards semantic search: facets
    • Building a search engine on top of metadata is difficult
      • Intrinsic quality problems: correctness, coverage
    • Especially when data is so heterogeneous
      • 100s of formats
      • From flat 5-fields records to 100-nodes XML trees
      • Language issue!
    • We currently use a simple interoperability format
      • Quick-win showing quickly its limits
    • We can better use institutions’ original metadata
    • Accommodate their different practices
      • Data structures and semantics
    • Access objects via a semantic layer of vocabularies for subjects, persons, places…
    Semantic ThoughtLab: experimenting solutions
  • Towards semantics-enabled search
    • Building a "semantic layer" to help accessing content
  • Towards semantics-enabled search
    • Enhance access to Europeana content by semantics
      • Query expansion, clustering of results
    • Exploiting various types of relations
      • "located in", "lived in", "is more specific concept"…
    • Semantics are already there, in metadata and "controlled vocabularies" used in metadata
      • Thesauri, classifications…
    • Requires to make it properly machine-accessible
  • Prototype: Europeana Thought Lab
      • http://europeana.eu/portal/thought-lab.html
  • Semantic auto-completion
  • Clustering of results
  • Baseline: matching concepts' label Controlled place name from a vocabulary at the Rijskmuseum Metadata for the object
  • A "more specific Egypte"?
  • A "more specific Egypte"? Metadata for the object
  • A place more specific than the Egypt one Semantic information on the Giza place in the Rijskmuseum Vocabulary
  • Following other relations
  • Following other relations - creator Metadata for the object Controlled person name from a vocabulary at the Rijskmuseum
  • Following other relations - match Information on Gustave Le Gray from the Rijskmuseum Vocabulary Matched to a "Gustave Le Gray" from another Vocabulary
  • Following other relations – death place Information on Gustave Le Gray from the Union List of Artist Names (Getty)
  • Following other relations – death place Information on Cairo from the Thesaurus of Geographic Names (Getty) Matched to "Cairo" from another vocabulary…
    • A hell of relations?
    • Well, they were in the original data, we just had to make them explicit!
    • Cultural Heritage institution often have a wealth of metadata to share and exploit
  • Enabling bits & pieces
    • Exploiting semantic links in CH vocabularies
      • Rijksmuseum thesaurus:
      • Concept “Giza” narrower than concept “Egypte”
    • Mapping/alignment between CH vocabularies
      • Louvre’s “Égypte” equivalent to Rijksmuseum’s “Egypte”
    • Enrichment of existing metadata
      • The string “Egypt” in a metadata record indicates the concept of Egypt defined in Rijksmuseum thesaurus
  • SKOS, Knowledge Organization Systems and Linked Data
    • SKOS allows representing (simple) KOS data as RDF
    animals NT cats cats UF domestic cats RT wildcats BT animals SN used only for domestic cats domestic cats USE cats wildcats
  • SKOS, KOSs and LD
    • SKOS allows bridging across KOSs from different contexts
    http://www.w3.org/2004/02/skos/
  • SKOS is used!
    • Many Libraries – not a surprise!
      • Swedish National Library’s Libris catalogue and thesaurus http://libris.kb.se/
      • Library of Congress’ vocabularies, including LCSH http://id.loc.gov/
      • DNB’s Gemeinsame Normdatei (incl. SWD subject headings) http://d-nb.info/gnd/
        • Documentation at https://wiki.d-nb.de/display/LDS
      • BnF’s RAMEAU subject headings http://stitch.cs.vu.nl/
      • OCLC’s DDC classification http://dewey.info/ and VIAF http://viaf.org/
      • STW economy thesaurus http:// zbw.eu/stw
      • National Library of Hungary’s catalogue and thesauri http:// oszkdk.oszk.hu/resource/DRJ/404 (example)
    • Other fields
      • Wikipedia categories through Dbpedia http://dbpedia.org/
      • New York Times subject headings http://data.nytimes.com/
      • IVOA astronomy vocabularies http://www.ivoa.net/Documents/latest/Vocabularies.html
      • GEMET environmental thesaurus http://eionet.europa.eu/gemet
      • UMTHES
      • Agrovoc http://aims.fao.org/
      • Linked Life Data http://linkedlifedata.com/
      • Taxonconcept http://www.taxonconcept.org/
      • UK Public sector vocabularies http://standards.esd.org.uk/ (e.g., http://id.esd.org.uk/lifeEvent/7 )
  • KOS Alignments?
    • Quite many of them are linked to some other resource
    • LCSH, SWD and RAMEAU interlinked through MACS mappings
    • GND linked to DBpedia and VIAF
    • Libris linked to LCSH
    • Agrovoc to CAT, NAL, SWD, GEMET
    • NYT to freebase, DBpedia, Geonames
    • dbPedia links are overwhelming
      • Hungary, STW, TaxonConcept, GND…
  • Enabling bits & pieces (c’ed)
    • Appropriate data model for objects
      • Generic constructs for creation, title, subject, etc. that are useful for querying
    • Flexible data model
      • SW ontology linking features allow to keep close to original data while having the generic notions above
  • Formal semantics, metadata schemas and querying
    • The query:
    • The existing description:
    • Why is there a match?
    • For the Europeana ontology, every rma:depicts statement implies a vra:subject statement
    rma: gezicht_in_cairo rma:Cairo rma:depicts rma:Egypt skos:broader ?x ?y vra:subject rma:Egypt skos:broader
  • Where are the challenges?
    • Semantic conversion of data
      • Using appropriate data models
      • Enriching legacy metadata
    • Semantic alignments
      • Between description ontologies
        • vra:depicts rdfs:subPropertyOf dc:subject
      • Between concepts in controlled vocabularies
        • iconclass:bird skos:closeMatch ddc:bird
  • Alignment of semantic references
  • Where are the challenges?
    • Semantic alignment (c'ed)
      • Find correspondences between large vocabularies
      • In a multilingual context
    • Scalability
      • Plugging the semantic features into the Europeana production environment
  • The Europeana Data Model (EDM) with input from Carlo Meghini, Guus Schreiber, Stefan Gradmann, Maxx Dekkers, Steffen Hennicke, Viktor de Boer et al. from Europeana V1
  • Rationale of EDM
    • Precursor: ESE (Europeana Semantic Elements)
      • represents lowest common denominator for object metadata
        • convert datasets to Dublin-Core like standard
      • forces interoperability
      • major drawback: original metadata is lost
      • most values are simple strings
    • EDM goals
      • preserve original data while still allowing for interoperability
      • Semantic Web representation
    • A community-driven effort
      • C ore experts, validation by representatives of various CH domains
  • EDM requirements & principles
    • Distinction between “provided object” (painting, book, program) and digital representation
    • Distinction between object and metadata record describing an object
    • Allow for multiple records for same object, containing potentially contradictory statements about an object
    • Support for objects that are composed of other objects
    • Standard metadata format that can be specialized
    • Standard vocabulary format that can be specialized
    • EDM should be based on existing standards
  • EDM basics
    • OAI ORE for organization of metadata about an object
    • Dublin Core for metadata representation
    • SKOS for vocabulary representation
    • + Links to CIDOC-CRM and other shared ontologies
  • Dublin Core
    • EDM uses the latest version of DCMI Metadata Terms for a core of semantically interoperable properties
      • And for backward compatibility, cf. ESE
    • Specified with an RDF model
    • Specialization of 15 original DC elements
    • Can be specialized itself
      • see requirement -> this is a crucial distinction with ESE
    • Used in the richest way possible
      • Pointers to resources
  • SKOS: vocabulary publication on the Web
    • Already seen…
  • OAI ORE
    • Specification:
    • http://www.openarchives.org/ore/1.0/toc.html
    • Specified with an RDF model
    • Four key notions (RDF classes)
      • Object : the book/painting/program being described
      • Aggregation : organizes object information from a particular provider (museum, archive, library)
      • Proxy : the object as viewed in a metadata record
      • Digital representation : some digital form of the object with a Web address
  • The Example - 1
  • The Example - 2
  • Aggregation organizes data of a provider aggregation digital representation object provenance metadata
  • Proxy: metadata record for an object proxy object metadata
  • Multiple aggregations = multiple providers aggregation of DMF aggregation of Louvre
  • Multiple aggregations = multiple providers DMF proxy Louvre P roxy Louvre title DMF title The “real” painting
  • Europeana is “just” a special provider with processed/enriched metadata Europeana aggregation enriched metadata Europeana landing page
  • A flexible model: different semantic grains
    • Cf. goal: “preserve original data while still allowing for interoperability”
    • Keep data expressed as close as possible to original model
    • Using mappings to more interoperable level
  • A flexible model: objects, events and the rest
    • Preserving and exploiting original data also means being compatible with descriptions beyond simple object level
    • Also crucial for semantic enrichment
  • A flexible model: object and events (2)
    • Classes and Properties for event-, agent-, place-centric modeling
    • Instances of (local) vocabularies using skos:Concept
    • Using RDF, EDM allows any kind of network to be attached to a provided object.
  • A flexible model: object and events (3)
  • Advanced modeling in EDM
    • Relations between provided objects
      • Part-whole links for complex (hierarchical) objects
      • Derivation and versioning relations
      • Relations between provided objects, for instance artistic derivation between works;
        • ens:isRepresentationOf
        • ens:isNextInSequence
  • Linked data and cultural heritage?
  • The case for linked data in cultural heritage
    • Not just a more sophisticated way to represent data!
    • Ease of getting data from external sources
      • Just going to the URI and fetch the RDF there
    • Ease of publishing data
      • Linked data as a dissemination channel for Europeana data
    • Ease of linking across datasets
      • Linked data as a dissemination channel for Europeana data
    • Object identification as cornerstone
      • Records are just a side feature!
    • From a movement supported by researchers
    • To much wider awareness
      • Open government initiatives, libraries…
    • Continuing effort: show benefits of collaborating to a cultural heritage data web
    • Library Linked Data W3C incubator
      • http://www.w3.org/2005/Incubator/lld
    Encouraging open linked data adoption
  • Linked Library Cloud beginning 2008 [Ross Singer, Code4Lib2010] http://code4lib.org/conference/2010/singer
  • Linked Library Cloud mid-2010
    • Plus:
    • Germany NL
    • Hungary NL
    • STW
    • GEMET
    • NYT
    • Agrovoc
    [Ross Singer, Code4Lib2010] http://code4lib.org/conference/2010/singer
  • Is that a surprise?
    • Not really, let’s have a look at a real-world case…
  • Johan Stapel, Koninklijke Bibliotheek KOS & collection environment @KB
    • A broad range of datasets
    • That describe the same objects
    • Or related objects
    • Which are about similar subjects
    • Which were made by the same persons
    • Or related persons
    • In the same places
    • Etc…
  • Thanks!
    • [email_address]
    • Europeana.eu team
    • Web and Media lab @ Vrije Universiteit Amsterdam
      • http://wiki.cs.vu.nl/web-media
    • EuropeanaConnect project
      • http://www.europeanaconnect.eu/