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• Is about using the Web to create typed links between data from different sources
• Refers to data published on the Web in such a way that– It is machine-readable– Its meaning is explicitly defined– It is linked to other datasets– It can be linked to from external datasets
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Properties of the Web of Data
• It is generic– Can contain any type of data• Data about anything
– Anyone can publish data– No constraints on choice of vocabularies– entities are connected by RDF links
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A Taste of Linked Data
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A Taste of Linked Data (Cont.)
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Linked Data Technology Stack
URI
HTTPRDFS / OWL
RDF / RDF Links
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Ontology , RDF
• Ontology provides a means to vocabularies and link’s semantics on linked data.
• RDF provides a generic, graph-based data model to structure and link data that describes things
• A triple [subject, predicate, object]– Subject: a URI– Predicate: a URI– Object: a URI or a string literal
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LOD Cloud : May 2007
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LOD Cloud : July 2007
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LOD Cloud : August 2007
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LOD Cloud : November 2007
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LOD Cloud : February 2008
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LOD Cloud : March 2009
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LOD Cloud : July 2009
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LOD Cloud : September 2010
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LOD Cloud : September 2011
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Retrieval Process
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• a) Query construction• b) Search algorithm of the system• c) Presentation of the results
Search EnginesQuery A lot of related Web Pages
QA SystemsQuestion Exact Answer
Retrieval Process (Cont.)
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Query Analyzer
Query
A lot ofWeb Pages
WWW
Crawler
RequestWeb Pages
IndexFile
Indexer
Web Pages
Index TermsSearch
Ranking
Results DocDatastore
Web Pages
UI
Query
Ranked Results
Web Pages
• Traditional SE
Some Problems
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• Information search with search engines
Therefore, what is needed?
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• Assign meta data to information objects• Content description with concepts and relations between
them• Provision of background knowledge• Provision of the semantics of relations for query
extension, ontology integration, etc.
RDF
RDF Schema, OWL, Rules
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Question Answering
• Question answering (QA) systems take users’ natural language questions and automatically locate answers from large collections of documents.
• Two types of QA systems– Closed-Domain (or restricted domain) Question Answering– Open-Domain Question Answering