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Klausur

Klausur. Wann: Freitag 16. Februar 2007 Start: 10:00 Uhr Dauer: 120 Minuten Ort: Magnushörsaal Ihr braucht: Stift(e), Lichtbildausweis, Studentenausweis!. Semantic Web. Tolle. ?. ?. ?. ?. ?. Die Situation im Internet. Möglichkeiten heutiger Internetsuchmaschinen sind begrenzt.

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Klausur

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  1. Klausur • Wann: Freitag 16. Februar 2007 • Start: 10:00 Uhr • Dauer: 120 Minuten • Ort: Magnushörsaal • Ihr braucht: Stift(e), Lichtbildausweis, Studentenausweis!

  2. Semantic Web

  3. Tolle ? ? ? ? ? Die Situation im Internet • Möglichkeiten heutiger Internetsuchmaschinen sind begrenzt.

  4.  führte bei Google zu mehr als 143.000 Treffern ???? Ende 2005 Die Situation im Internet • Mögliche Suchanfrage:Tolle Universität Jan. 2007: 1.210.000 Treffer

  5. Die Situation im Internet • Keine Vernetzung der Informationen! arbeitet an ist Vater von

  6. predicate subject object Die Situation mit dem Semantischen Web • Vernetzung der Informationen! + arbeitet an URI für „Karsten Tolle“ + ist Vater von

  7. Semantic Web • "The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation." -- Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web, Scientific American, May 2001

  8. Maschinenverständliche Informationen • Nicht durch KI • Möglichkeit: Maschinen sollen fähig sein ein definiertes Problem mit definierten Operationen auf existierenden, definierten Daten zu lösen! • Voraussetzung: von maschinenlesbaren Daten zu maschinenverständlichen Daten • Nutzung von Metadaten (Daten über Daten)

  9. RDF als Grundlage • RDF – Resource Description Framework Framework zur Beschreibung von (Web) Ressourcen, bietet einheitliche Konventionen für: • Syntax • Struktur • Semantik

  10. zeitliche Entwicklung

  11. Repräsentationsformen • Graph – zum Lesen durch den Menschen • Triple – skalierbare Darstellung, einfach zu speichern • RDF/XML – für den Datenaustausch Bemerkung: es gibt eine 1-1 Abbildung zwischen diesen Repräsentationsformen!

  12. Ziele bei der Entwicklung von RDF • Independence (Unabhängigkeit). It should be possible for anyone to define its own schemas and use and/or reuse them in a specific semantic way. • Interchange (Austauschbarkeit). It should be easy to transport and storage the metadata described by RDF. • Scalability (Skalierbarkeit). Even for a huge set of metadata it should be easy to handle and process them.

  13. RDF Datenmodell • RDF Data Model is based on the notions of resource, property, literal and statement • resource  everything is a resource! • property specific characteristics of a resource; properties are resources! • literal constant value represented by character strings • statement a specific resource together with a property and a value (either a resource or a literal), respectively called subject, predicate and object • Bemerkung: Früher waren Literale und Resourcen getrennt!

  14. Grafische Darstellung von RDF-Aussagen

  15. Tripeldarstellung: [ http://www.dbis.cs.uni-frankfurt.de/~tolle/RDF/index.html http://www.my.de/vok#creator „Karsten Tolle“ ] Graf: RDF/XML: <?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:my="http://www.myns.de/vok#" > <rdf:Description rdf:about="http://www.dbis.cs.uni-frankfurt.de/~tolle/RDF/index.html"> <my:creator>Karsten Tolle</my:creator> </rdf:Description> </rdf:RDF>

  16. Tripeldarstellung: [ http://www.dbis.cs.uni-frankfurt.de/~tolle/RDF/index.html my:creator _:1 ] [ _:1 rdf:type my:Person ] [ _:1 my:name “Karsten Tolle” ] Graf: RDF/XML: <?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:my="http://mytestnamespace#" > <rdf:Description rdf:about="http://www.dbis.cs.uni-frankfurt.de/~tolle/RDF/index.html"> <my:creator> <my:Person> <my:name>Karsten Tolle</my:name> </my:Person> </my:creator> </rdf:Description> </rdf:RDF>

  17. RDF/XML <?xml version="1.0" ?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:ex="http://example.org/stuff/1.0/"> <rdf:Description rdf:about="http://www.dbis.informati.uni-frankfurt.de/~tolle/RDF/index.html"dc:title="Semantic Web and the Resource Description Framework (RDF) at DBIS"> <ex:editor> <rdf:Description ex:fullName="Karsten Tolle"> <ex:homePagerdf:resource="http://www.dbis.informati.uni-frankfurt.de/~tolle/"/> </rdf:Description> </ex:editor> </rdf:Description> </rdf:RDF>

  18. Graph RepresentationIsaViz

  19. RDF Schema mechanism • Based on the basic notation of using statements, RDF defines a schema mechanism that introduces the basic constructs that can be used in the definition of RDF schemas (or vocabularies) • An RDF schema can define for a given application or domain • resources • classes • properties along with some constraints • hierarchies for classes and properties • collections or containers • annotations to the defined vocabulary

  20. War in der 1999 Spezifikation anders! Geloescht Geloescht superclass of RDF Schema mechanism (classes) • There are two namespaces defined for RDF that can be viewed as the core vocabulary. We abbreviate them by the prefix: rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdfs = "http://www.w3.org/2000/01/rdf-schema#"

  21. RDF Schema mechanism (core properties) • rdf:type – instantiates a resource into a class • rdfs:subClassOf – used to define a class hierarchy • rdfs:subPropertyOf – used to define a property hierarchy • rdfs:domain – constraints defines a property to be used with subject-resources of a specified class • rdfs:range – constraints defines a property to be used with object of a specified class • ...

  22. RDF/XML Schema A part of rdfs (http://www.w3.org/2000/01/rdf-schema): ... <rdf:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#type"> <rdfs:isDefinedByrdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#" /> <rdfs:label>type</rdfs:label> <rdfs:comment>The subject is an instance of a class.</rdfs:comment> <rdfs:rangerdf:resource="http://www.w3.org/2000/01/rdf-schema#Class" /> <rdfs:domainrdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource" /> </rdf:Property> <rdfs:Class rdf:about="http://www.w3.org/2000/01/rdf-schema#Class"> <rdfs:isDefinedByrdf:resource="http://www.w3.org/2000/01/rdf-schema#" /> <rdfs:label>Class</rdfs:label> <rdfs:comment>The class of classes.</rdfs:comment> <rdfs:subClassOfrdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource" /> </rdfs:Class> ...

  23. Reified Statements-Aussagen über Aussagen

  24. Reified Statements Vassilis says: ”Karsten is the creator of the resource http://www.ics.forth.gr/proj/isst/RDF.”

  25. Container Three types: • rdf:Bag – a unordered set {a, b, c, d} • rdf:Seq – an ordered set [a, b, a, c] • rdf:Alt – an alternative (rdf:_1 is default)

  26. Container

  27. Collection

  28. Container vs Collection • With a collection you can ensure (when using correct structure) that all elements are contained. • Containers have a semantic, collections not. Problem: The creator of an RDF file needs to choose between these two constructs.

  29. page Karsten creator RDF vs XML How to represent this information in XML? <document> <uri>page</uri> <creator>Karsten</creator> </document> <creator ID="Karsten"> <document uri="page"/> </creator> <uri ID="page" type="document"> <creator ID="Karsten"/> </uri> <document uri="page" creator="Karsten" />

  30. RDF vs XML <a> <b attr1="344"> <c>ttttttt</c> <d>uuuuu</d> </b> <e attr2="vvvvvvv"/> </a> Without knowing the schema you only have the structure!

  31. RDF vs XML XML Schemas ... Model RDFSchema

  32. RDF vs XML • In XML you have • A many to one mapping. • You need to know the schema. • Limited to a tree. • No inference defined. • No default constructs like in RDF like classes and hierarchies, containers, ...) • ...

  33. RDF Limitations • No equivalence • needed to resolve synonymy • No distinction between schemas and data • anyone can add to schema definitions • Weak schema versioning mechanism • schemas will evolve over time

  34. Extensions for RDF • OWL – Web Ontology Language • OWL lite • OWL DL (description logics) • OWL full • Namespace: xmlns:owl ="http://www.w3.org/2002/07/owl#"

  35. OWL Lite (some examples) (In)Equality: • equivalentClass • equivalentProperty • sameAs • differentFrom • allDifferent Property Characteristics: • inverseOf • TransitiveProperty • SymmetricProperty • FunctionalProperty • InverseFunctionalProperty

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