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Standards for the Representation of Knowledge on the Semantic Web

Standards for the Representation of Knowledge on the Semantic Web. Antoine ISAAC STITCH Project Offene Archivierbare Formate Oct. 25 th , 2007. Agenda. Interoperability problems in Cultural Heritage An introduction to the Semantic Web The problem RDF RDFS/OWL Why is it interesting?

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Standards for the Representation of Knowledge on the Semantic Web

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  1. Standards for the Representation of Knowledge on the Semantic Web Antoine ISAAC STITCH Project Offene Archivierbare Formate Oct. 25th, 2007

  2. Standards for the Representation of Knowledge on the Semantic Web Agenda • Interoperability problems in Cultural Heritage • An introduction to the Semantic Web • The problem • RDF • RDFS/OWL • Why is it interesting? • Porting existing metadata to the Semantic Web • SKOS • Conclusion: SW and semantic alignment

  3. Standards for the Representation of Knowledge on the Semantic Web Agenda • Interoperability problems in Cultural Heritage • An introduction to the Semantic Web • The problem • RDF • RDFS/OWL • Why is it interesting? • Porting existing metadata to the Semantic Web • SKOS • Conclusion: SW and semantic alignment

  4. Standards for the Representation of Knowledge on the Semantic Web The Interoperability Problem in Cultural Heritage • STITCH • SemanTic Interoperability To access Cultural Heritage • Here, CH at large (incl. Digital Libraries) • Trend: simultaneous access to different collections • The European Library, Memory of the Netherlands • Problem: how to access seamlessly different collections? • Traditional solution: using object metadata • But…

  5. Standards for the Representation of Knowledge on the Semantic Web KB Illustrated Manuscripts

  6. Standards for the Representation of Knowledge on the Semantic Web KB Illustrated Manuscripts

  7. Standards for the Representation of Knowledge on the Semantic Web Mandragore

  8. Standards for the Representation of Knowledge on the Semantic Web Mandragore

  9. Standards for the Representation of Knowledge on the Semantic Web The Interoperability Problems From syntactic to semantic • Different formats • “We have a solution” • XML as a standard for data exchange • Different metadata schemes • “Something is coming” • Dublin Core for MD exchange

  10. Standards for the Representation of Knowledge on the Semantic Web The Interoperability Problems From syntactic to semantic (continued) • Different conceptual vocabularies for description • “Do you really want to discuss about it now?” • No standard vocabulary • DDC, UDC, SWD, LCSH, AAT, Iconclass and myriads of others… • Not even a common model for these Knowledge Organization Schemes (KOSs) • thesauri, classification schemes, subject heading lists… • Even worse: there are reasons for this!

  11. Standards for the Representation of Knowledge on the Semantic Web The result

  12. Standards for the Representation of Knowledge on the Semantic Web An Ideal Situation

  13. Standards for the Representation of Knowledge on the Semantic Web Agenda • Interoperability problems in Cultural Heritage • An introduction to the Semantic Web • The problem • RDF • RDFS/OWL • Why is it interesting? • Porting existing metadata to the Semantic Web • Conclusion: SW and semantic alignment

  14. Standards for the Representation of Knowledge on the Semantic Web Why thinking of the Semantic Web? • Cf Semantic Web activity page at W3C • http://www.w3.org/2001/sw/ • “The Semantic Web provides a common framework that allows data to be shared and reused” • “The Semantic Web is a web of data” • “It is about common formats for integration and combination of data drawn from diverse sources”

  15. Standards for the Representation of Knowledge on the Semantic Web SW Problem: The Web for Humans • A city • A flag • The city’s location Meaning

  16. Standards for the Representation of Knowledge on the Semantic Web SW Problem: The Web for Humans

  17. Standards for the Representation of Knowledge on the Semantic Web SW Problem: The Web for Computers? • Characters • Images Black boxes • Markup Layout/Display

  18. Standards for the Representation of Knowledge on the Semantic Web SW Problem: The Web for Computers?

  19. Standards for the Representation of Knowledge on the Semantic Web The Interoperability Problems in CH (reminder)

  20. Article Document The_Netherlands subClassOf type hasCapital file1 partOf Amsterdam type par3 subject City Standards for the Representation of Knowledge on the Semantic Web The Semantic Web Approach: A Web of (Meta)data

  21. Standards for the Representation of Knowledge on the Semantic Web A footnote • Why “(meta)data”? • Because what is metadata for certain applications can indeed be the data for the Semantic Web • Boundary is blurred

  22. Standards for the Representation of Knowledge on the Semantic Web Agenda • Interoperability problems in Cultural Heritage • An introduction to the Semantic Web • The problem • RDF • RDFS/OWL • Why is it interesting? • Porting existing metadata to the Semantic Web • Conclusion: SW and semantic alignment

  23. Standards for the Representation of Knowledge on the Semantic Web The Semantic Web (1/4) • Pointing at resources • What?Knowledge objects, everything that we may want to refer to (including documents) • How? Uniform Resource Identifiers (incl. URLs)

  24. Standards for the Representation of Knowledge on the Semantic Web A Web of Resources myVoc1:Article http://ex.org/files/file1 myVoc2:Amsterdam http://ex.org/files/file1#par3 http://www.ned.nl/rep321

  25. Standards for the Representation of Knowledge on the Semantic Web The Semantic Web (2/4) • Pointing at resources: URIs • Creating structured assertions involving resources • What?Structured assertions with typed links • How?RDF (Resource Description Framework) Factual knowledge encoded as “triples” subject – predicate (property) – object http://ex.org/files/file1#par3 myVoc1:subject myVoc2:Amsterdam

  26. Standards for the Representation of Knowledge on the Semantic Web Data in an RDF “graph” myVoc1:Article rdf:type http://ex.org/files/file1 myVoc2:Amsterdam myVoc1:partOf myVoc1:subject http://www.ned.nl/rep321 http://ex.org/files/file1#par3

  27. Standards for the Representation of Knowledge on the Semantic Web Agenda • Interoperability problems in Cultural Heritage • An introduction to the Semantic Web • The problem • RDF • RDFS/OWL • Why is it interesting? • Porting existing metadata to the Semantic Web • Conclusion: SW and semantic alignment

  28. Standards for the Representation of Knowledge on the Semantic Web The Semantic Web (3/4) • Pointing at resources: URIs • Enabling structured assertions: RDF • Giving machine-understandable semantics to “building blocks” • What? Ontologies • “Formal definitions of shared conceptual vocabularies” • Giving semantics for properties and classes • How? RDFS /OWL(Ontology Web Language)

  29. Standards for the Representation of Knowledge on the Semantic Web RDF Schema (RDFS) • Meta-language to create vocabularies • “Article” is an (RDFS) Class • Denotes a type, a collection of resources (individuals) • “subject” is an (RDFS) Property • Giving semantics to vocabulary elements • My “Article” has the literal article as a label for display • myVoc1:Article rdfs:label “article” • “Article” is a subclass of the class “Document” • myVoc1:Article rdfs:subClassOf myVoc1:Document • “subject” is applied to resources of type “Document” • myVoc1:Article rdfs:domain myVoc1:Document

  30. Standards for the Representation of Knowledge on the Semantic Web RDF Schema (RDFS) • Different kind of constructs • Assigning domain and ranges of properties • Creating hierarchies of classes and properties • Labels and informal specifications • (Some) Equipped with formal semantics • R rdf:type C1, C1 rdfs:subClass C2 -> X rdf:type C2 • P rdfs:domain C, R1 P R2 -> R1 rdf:type C

  31. Standards for the Representation of Knowledge on the Semantic Web Web Ontology Language (OWL) • Same function as RDFS, but more possibilities, e.g. • Characteristics of properties • Inverse(hasAuthor, authorOf) • Restriction on property usage • SubClassOf(Books, restriction(hasISBN minCardinality(1))) • Combination and exclusion of classes and properties • DisjointClasses(Persons, Books) • Inherits from AI research and Description Logics • Comes in different levels of complexity: • Lite, DL, Full

  32. Standards for the Representation of Knowledge on the Semantic Web Tools to build RDFS/OWL ontologies

  33. Standards for the Representation of Knowledge on the Semantic Web Ontological information rdfs:subClassOf myVoc1:Article myVoc1:Document rdf:type http://ex.org/files/file1 myVoc2:Amsterdam myVoc1:partOf myVoc1:subject http://ex.org/files/file1#par3 http://www.ned.nl/rep321

  34. Standards for the Representation of Knowledge on the Semantic Web The Semantic Web (4/4) • Pointing at resources: documents, knowledge objects • Enabling structured assertions • Using “building blocks” with precise semantics • Controlling existing facts, inferring new ones Part of the tasks are delegated from the user to inference engines that use the formal semantics of ontologies

  35. Standards for the Representation of Knowledge on the Semantic Web Ontological information rdfs:subClassOf myVoc1:Article myVoc1:Document rdf:type rdf:type http://ex.org/files/file1 myVoc2:Amsterdam myVoc1:partOf myVoc1:subject http://ex.org/files/file1#par3 http://www.ned.nl/rep321

  36. Standards for the Representation of Knowledge on the Semantic Web RDFS/OWL and Semantic Interoperability

  37. Standards for the Representation of Knowledge on the Semantic Web Agenda • Interoperability problems in Cultural Heritage • An introduction to the Semantic Web • The problem • RDF • RDFS/OWL • Why is it interesting? • Porting existing metadata to the Semantic Web • Conclusion: SW and semantic alignment

  38. Standards for the Representation of Knowledge on the Semantic Web Why is it interesting? • RDF model is simple • Just triples • There is meaning exploitable by computers • Resources are universal, hence shareable • One resource for one object, used in different places • Vocabularies for (meta)data are made of resources • They can be re-used in different applications • RDF does not enforce the use of a specific ontology • Their meaning (incl. formal semantics) is shareable

  39. Standards for the Representation of Knowledge on the Semantic Web Building on top of the Web • Web-based resources allow distribution/sharing of • document • vocabulary • (meta)data http://www.geo.org/voc/ (par3, subject, Amsterdam) http://www.kb.nl/eDepot http://www.ned.nl/rep321 different owners & locations

  40. Standards for the Representation of Knowledge on the Semantic Web Why is it interesting? • Using open standards • W3C’s URI, XML, RDF, RDFS, OWL

  41. Standards for the Representation of Knowledge on the Semantic Web Footnote: Building on top of XML • RDF can be encoded as XML data • RDF/XML is the reference syntax, but others are possible <rdf:Descriptionrdf:about=”http://www.ned.nl/doc321”> <myVoc1:subjectrdf:resource=” http://www.geo.org/Amsterdam”/> </rdf:Description> <rdf:Descriptionrdf:about=”http://www.geo.org/The_Netherlands”> <myVoc2:hasCapitalrdf:resource=”http://www.geo.org/Amsterdam”/> </rdf:Description>

  42. Standards for the Representation of Knowledge on the Semantic Web Agenda • Interoperability problems in Cultural Heritage • An introduction to the Semantic Web • The problem • RDF • RDFS/OWL • Why is it interesting? • Porting existing (meta)data to the Semantic Web • SKOS • Conclusion: SW and semantic alignment

  43. Standards for the Representation of Knowledge on the Semantic Web Problem: Data Population • How will Semantic Web data will be created? • Creation of “born-semantic” data? • Automatic or manual (tagging) • Converting existing databases to SW format • Fits the vision of the SW as a place to exchange data • In the CH situation: porting legacy metadata is fundamental

  44. Standards for the Representation of Knowledge on the Semantic Web Porting CH Metadata to the Semantic Web • Requirement: an ontology to create SW-enabled representations for metadata • “Ontologized” metadata schema • A first candidate: Dublin Core for metadata schema • Well-established set of metadata elements • Already coming in RDFS!

  45. Standards for the Representation of Knowledge on the Semantic Web Porting KOSs to the Semantic Web • How about metadata values from Knowledge Organization Schemes? • E.g. dc:subject values (terms, keywords, classes…) • DC does not address the problem of KOS representation • Why is it important? • Their heterogeneity is a primary source of interoperability problems • They are provided with (informal) semantics • Taxonomies, associative networks can be exploited in many applications

  46. Standards for the Representation of Knowledge on the Semantic Web Porting KOSs to the Semantic Web • A first solution: converting KOSs to formal ontologies • Ontologization of terms/concepts into classes • Problem: KOSs are generally no full-fledged ontologies • Iconclass: “Group of Birds” rdfs:subClassOf “Birds”? • There is much work needed to have semantics fit! • The concept of a car (reference=a subject in a KOS) vs. the class of cars (reference=a set of objects in the world) • Things in ontologies and KOSs don’t have the same epistemological status • We need a model for elements of the realm of subjects

  47. Standards for the Representation of Knowledge on the Semantic Web Representing KOSs – Requirements Many different models and formats to represent vocabularies • Need for standard formats to develop standardized tools and methods • Semantic correspondences • Browsing/information retrieval tools using vocabularies • Need to represent features commonly used by these tools • Especially lexical information and semantic links

  48. Standards for the Representation of Knowledge on the Semantic Web SKOS (Simple Knowledge Organisation System) • Model to represent KOSs (thesauri, classification schemes) on the Semantic Web in a simple way • Comparable to Dublin Core, for conceptual vocabularies • SKOS offers building blocks to create XML/RDF data • Concepts and ConceptSchemes • Lexical properties (prefLabel, altLabel) • Semantic relations (broader, related) • Notes (scopeNote, definition)

  49. Standards for the Representation of Knowledge on the Semantic Web SKOS: Iconclass Example

  50. Standards for the Representation of Knowledge on the Semantic Web SKOS: Limitations • SKOS is a standard • Simple • Meant for information exchange and re-use • Not everything can be represented! E.g. for Iconclass, difficulty to represent all types of auxiliaries • Keys, structural digits… • It is still work in progress • W3C Semantic Web Deployment Working Group

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