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

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

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

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…

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

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

Standards for the Representation of Knowledge on the Semantic Web Mandragore

Standards for the Representation of Knowledge on the Semantic Web Mandragore

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

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!

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

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

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

Standards for the Representation of Knowledge on the Semantic Web Why thinking of the Semantic Web? Cf Semantic Web activity page at W3C “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”

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

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

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

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

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

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

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

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

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)

Standards for the Representation of Knowledge on the Semantic Web A Web of Resources myVoc2:Amsterdam myVoc1:Article

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 myVoc1:subject myVoc2:Amsterdam ar3

Standards for the Representation of Knowledge on the Semantic Web Data in an RDF “graph” myVoc1:subject myVoc2:Amsterd am myVoc1:partOf myVoc1:Article rdf:type

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

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)

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

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

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

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

Standards for the Representation of Knowledge on the Semantic Web Ontological information myVoc1:subject myVoc2:Amsterd am myVoc1:Article rdf:type myVoc1:partOf myVoc1:Document rdfs:subClassOf

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

Standards for the Representation of Knowledge on the Semantic Web Ontological information myVoc1:subject myVoc2:Amsterd am myVoc1:Article rdf:type myVoc1:partOf myVoc1:Document rdfs:subClassOf rdf:type

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

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

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

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 (par3, subject, Amsterdam) different owners & locations

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

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

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

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

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!

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

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

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

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 Concept s and ConceptScheme s Lexical properties ( prefLabel, altLabel ) Semantic relations ( broader, related ) Notes ( scopeNote, definition )

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

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

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

Standards for the Representation of Knowledge on the Semantic Web What have we seen? TODO

Standards for the Representation of Knowledge on the Semantic Web Back to the Problem: Semantic Alignment Different ontologies/individuals should be aligned at the semantic level Using the same resources to join SW graphs together Using the same vocabularies and semantics But: difficulty to recognize equivalent resources at data creation time There is (and will be) no such thing as a single one ontology! A posteriori semantic alignment is needed

Standards for the Representation of Knowledge on the Semantic Web Back to the Problem: semantic alignment Fortunately, SW languages give appropriate means Equivalence/specialization links for properties and classes myVoc:auteur rdfs:subPropertyOf dc:creator myVoc:Article owl:equivalentClass yourVoc:Artikel Identity link for individuals vu:aisaac owl:sameAs kb:AntoineIsaac (yet unstable) SKOS mapping links for subjects iconclass:birds exactMatch swd:vogel But they don’t do the job for us! The links have to be created somehow This is another story…

Standards for the Representation of Knowledge on the Semantic Web Thank you!

Standards for the Representation of Knowledge on the Semantic Web Vocabulary alignment Find correspondences between vocabulary elements “klassieke ruïnes” ≈ “landschap met ruïnes” “maagd Maria” = “Heilige Moeder” STITCH aim: doing it (semi-)automatically Vocabularies are big They evolve over time Using techniques from Semantic Web research domain Problem comparable to ontology alignment Techniques already investigated there Linguistics, statistics

Standards for the Representation of Knowledge on the Semantic Web Automatic alignment techniques Lexical Structural Statistical Background knowledge

Standards for the Representation of Knowledge on the Semantic Web Lexical alignment Labels of entities, textual definitions tumor brainLongtumor Long More specific than

Standards for the Representation of Knowledge on the Semantic Web Automatic Alignment Techniques Lexical Structural Statistical Background knowledge

Standards for the Representation of Knowledge on the Semantic Web Statistical alignment Object information (e.g. book indexing) Thesaurus 1 Thesaurus 2 Collection of books “Dutch Literature” “Dutch”

Standards for the Representation of Knowledge on the Semantic Web Automatic Alignment Techniques Lexical Structural Statistical Background knowledge

Standards for the Representation of Knowledge on the Semantic Web Background knowledge Alignment using shared background knowledge Using a shared conceptual reference to find links Thesaurus 1 Thesaurus 2 “Calendar” “Publication”

Standards for the Representation of Knowledge on the Semantic Web Alignment: no universal solution No single technique gives an ideal solution Different techniques have to be selected/combined, depending on the application case Poor vs. rich semantic structure Extensive vs. limited lexical coverage Existence of collections described by several vocabularies Alignment is a difficult research problem

Standards for the Representation of Knowledge on the Semantic Web Conclusions : Alignement Les techniques simples permettent d'obtenir des résultats rapides concepts de Mandragore “accessibles” depuis Iconclass Leur fiabilité ne permet pas de les considérer comme sources uniques Combinaison avec travail manuel (vérification, complétion) L’alignement sémantique est toujours un problème de recherche difficile Aucune technique n’est parfaite Il faut sélectionner/combiner, en fonction des cas applicatifs

Standards for the Representation of Knowledge on the Semantic Web Demo mandraNewNONE, amphibienshttp://prauw.cs.vu.nl/rp33333/MANDRA-SV-ICE- mandraNewNONE Blé

Standards for the Representation of Knowledge on the Semantic Web Conclusions : Représentation Il est possible de produire des représentations WS standardisées (SKOS) des vocabulaires conceptuels Et des méta-données qui les utilisent Les techniques existantes pour accéder aux méta-données et vocabulaires (OAI-PMH, XML) facilitent le travail C’est utile Réutilisation/interopérabilité des composants applicatifs utilisant les vocabulaires Facilité de la représentation de liens avec des éléments extérieurs au vocabulaire représenté

Standards for the Representation of Knowledge on the Semantic Web Links STITCHhttp://stitch.cs.vu.nlhttp://stitch.cs.vu.nl Demo collections BNF Mangragorehttp://mandragore.bnf.frhttp://mandragore.bnf.fr KB illuminated manuscripts Library-originated integration projects: MSAC search interfacehttp://sigma.nkp.czhttp://sigma.nkp.cz MACS projecthttp://macs.cenl.orghttp://macs.cenl.org Semantic web links Semantic Web at W3C SKOS Semantic Web projects dealing with Cultural Heritage MuseumFinlandhttp:// eCulturehttp://e-culture.multimedian.nl / /

Standards for the Representation of Knowledge on the Semantic Web Demo (1) Subject vocabulary, collection 1 Subjects

Standards for the Representation of Knowledge on the Semantic Web Demo (2) Hierarchical path from root to selected subject Possible specialization for selected subject

Standards for the Representation of Knowledge on the Semantic Web Document from Collection 2 Semantic alignment of subjects activated Demo (3)

Standards for the Representation of Knowledge on the Semantic Web Demo (4) Subject from voc2 aligned to voc1:amphibians” Back