Semantic Web Technologies Lecture Dr. Harald Sack Hasso-Plattner-Institut für IT Systems Engineering University of Potsdam Winter Semester 2012/13 Lecture Blog: http://semweb2013.blogspot.com / This file is licensed under the Creative Commons Attribution-NonCommercial 3.0 (CC BY-NC 3.0 ) Dienstag, 22. Januar 13
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(13) Semantic Web Technologies - Linked Data & Semantic Search
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Semantic Web Technologies
LectureDr. Harald Sack
Hasso-Plattner-Institut für IT Systems EngineeringUniversity of Potsdam
Winter Semester 2012/13
Lecture Blog: http://semweb2013.blogspot.com/This file is licensed under the Creative Commons Attribution-NonCommercial 3.0 (CC BY-NC 3.0)
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Linked Data Principles
(3) When someone looks up a URI, provide useful information, using the standards (RDF, SPARQL)
• RDF as universal data model for publishing structured data on the Web
• Make all URIs in the RDF graph dereferencable• Avoid RDF constructs that cause problems in Linked Data
context
• RDF Reification• RDF Collections und Containers• unnamed Blank Nodes
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Linked Data Principles
(4) Include links to other URIs, so that they can discover more things.
• Link RDF references among data between different data sources, to find information related by content
• Relationship LinksLinks to external LOD Entitites related with the original entity
• Identity LinksLinks to external LOD Entities referring to the same object or concept
• Vocabulary LinksLinks to definitions of the original entity
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The application of the Linked Data Principles leads to a ,Web of Data‘
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Development of the ,Web of Data‘
May 2007
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Nov 2007
Development of the ,Web of Data‘
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Development of the ,Web of Data‘
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July 2009
Development of the ,Web of Data‘
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September 2010
Development of the ,Web of Data‘
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September 2011
300 Datasets 31B RDF Triples504M Links
Development of the ,Web of Data‘
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□Semantic Mashups are applications that use linked RDF data from various data sources
□ in difference to interfaces and exchange formats or ordinary Web APIs, Linked Data offers the following benefits:□ a flexible and standardized data format (RDF)□ standardized access mechanism (http)□ possibility to put links (RDF-Links) among different data sources
» enables navigation» is supported by search engines (Crawler)» enables expressive search facilities over the crawled data
and beyond
S. Auer, J. Lehmann, Ch. Bizer: Semantitsche Mashups auf Basis vernetzter Daten, in T. Pellegrini, A. Blumauer (Hrsg.): Social Semantic Web, Springer, 2009.
Semantic Mashups
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Linked Data Sources in the Web
□Native publication□ D2R-Server, OpenLink Virtuoso, Pubby, etc.
□ Implementation of Wrappers around existing applications / APIs□SIOC Exporter for Wordpress, Drupal, phpBB,...□RDF Book Mashup (Amazon API, Google Base-API,...)
□Linking Open Data Project□Semantic Web Education and Outreach W3C working group □Catalogue of all known sources of linked data with an open
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Browser for Linked Data
■Differences to arbitrary RDF-Browsers□RDF Data to be visualized does not necessarely reside in
local repository, but is distributed in the Web□ requires dynamic reload of RDF resources■Tabulator (Tim Berners-Lee, MIT-)
(T. Berners-Lee et al.: Tabulator: Exploring and analyzing linked data on the semantic web, in Proc. 3rd Int. Semantic Web User Interaction Workshop, 2006, http://swui.semanticweb.org/swui06/papers/Berners-Lee/Berners-Lee.pdf)
■ OpenLink RDF Data Explorer□enables visualization as graph, timeline, map, etc.
Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
The Web is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is.(...according to Douglas Adams)
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Language has its fa
llacies...
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in particular,
if we don‘t know the langua
ge
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4242 42 4224424242 42 424267
4.3 Semantic Search4.3.1 Information Retrieval 4.3.3 Semantic Analysis and Retrieval4.3.4 Exploratory Search
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Definition (first try)Semantic Search
4242244242 • Annotation of (text-based) metadata with semantic entities• Entity-based Information Retrieval• Make use of semantic relations, as e.g. content-based
similarities of relationships• Interoperable metadata via semantic annotations• for content-based description• for structural / technical description
(Multimedia Ontologies)
Overall Goal: Quantitative and qualitative improvement of Information Retrieval
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• MPEG-7 has been re-engineered to become an OWL-DL ontology (2007: Arndt et al., COMM model)
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Multimedia OntologiesSemantic Metadata
4242244242
• Localize a region → Draw a bounding box
• Annotate the content → Interpret the content → Tag ,Astronaut‘
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Multimedia OntologienSemantic Metadata
Example: Tagging with an MPEG-7 Ontology
Reg1
mpeg7:image
mpeg7:depicts
Man on the Moon
mpeg7:spatial_decomposition Reg1
mpeg7:StillRegion
rdf:type
mpeg7:depicts
dbpedia:Astronaut
mpeg7:SpatialMask
mpeg7:polygon
mpeg7:Coords
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Named Entity Recognition
Astronaut Person
Neil Armstrong
Science Occupation
Employment
is a is a
subClassOf
subClassOf
Entities
Classes
Named Entity Recognition„locating and classifying atomic elements...intopredefined categories such as names, persons, organizations, locations, expressions of time,quantities, monetary values, etc.“C.J.Rijsbergen, Information Retrieval (1979)
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Astronaut Person
Neil Armstrong
Science Occupation
Employment
is a is a
subClassOf
subClassOf
Named Entity Recognition
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Named Entity Recognition
Astronaut Person
Neil Armstrong
Science Occupation
Employment
is a is a
subClassOf
subClassOf
„Armstrong was the first man on the Moon.“ Text
Entity Mapping
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Astronaut
Named Entity Recognition
Person
Neil Armstrong
Science Occupation
Employment
is a is a
subClassOf
subClassOf
Text
rdfs:label Neil Armstrong
rdf:type dbpedia-owl:Astronaut
rdf:type foaf:Person
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Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität PotsdamTurmbau zu Babel, Pieter Brueghel, 1563
How to use semantic data in Retrieval?
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Semantic metadata enable an improvement of traditional keyword-based retrieval by(1) Query String Refinement
enables more precise or more complete search results(2) Cross Referencing
enables to complement search results with additional associated or similar information
(3) Exploratory Search enables visualization and navigation of the search space
(4) Reasoningenables to complement search results with implicitly given information
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4.3 Semantic Search4.3.1 Information Retrieval 4.3.3 Semantic Analysis and Retrieval4.3.4 Exploratory Search
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Searching is not always
just searching
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I‘m looking for the book „Brave New World“ by Aldous Huxley in the first German edition...
Brave New World. - Aldous H U X L E Y.
- The Albatros Continental Library, 47
(Hamburg usw., Albatros Verlag, 1933)
257 S. 8“
II 1, 2506, 34548
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I really liked „Brave New World“ by Aldous Huxley but how should I find what to read next...?
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Exploratory Search• What, if the user does not know, which query string to use?• What, if the user is looking for complex answers ?• What, if the user does not know the domain he/she is looking for?• What, if the user wants to know all(!) about a specific topic?
• ...,Browsing‘ instead of ,Searching‘• ...to find something by chance, i.e. Serendipity• ...to get an overview• ...enable content based navigation
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Gather knowledge about dbpedia:Brave_New_Worldand decide, which interesting fact to follow....
http://dbpedia.org/page/Brave_New_World
Enable Exploratory Search based on Linked Open Data