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Semantic Web Basics
Dominic DiFranzoPhD Student/Research AssistantRensselaer Polytechnic InstituteTetherless World Constellation
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http://tw.rpi.edu/portal/Mashathon
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Interwebs?
Internet – graph of computers connected to one another
Web – graph of documents hyper-linked to one another
Semantic web – graph of concepts/ideas/data linked together by named relations.
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RDF•Triple: Subject Predicate Object
•Use URI for universal naming
•New York has the postal abbreviation NY
•<urn:x-states:New%20York> <http://purl.org/dc/terms/alternative> "NY" .
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Linked Open Data
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serialize in many ways
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dcterms="http://purl.org/dc/terms/">
<rdf:Description rdf:about="urn:x-states:New%20York"> <dcterms:alternative>NY</dcterms:alternative>
</rdf:Description></rdf:RDF>
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Linking
•I found a new dataset and it has the following triple
•<http://dbpedia.org/page/New_York> <http://dbpedia.org/ontology/Place/otherName> “The Empire State” .
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owl:sameAS
•<urn:x-states:New%20York> <http://www.w3.org/2002/07/owl#sameAs> <http://dbpedia.org/page/New_York> .
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Semantic Mashup Workflow
•Take data (CSV, XSL)
•Convert it to RDF
•Load in triple store
•Query with Sparql
•Visualize results using standard off-the-shelf visualization tools (Google viz, Exhibit, etc)
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Conversion to RDF
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Sparql
•SPARQL is a query language for the Semantic Web.
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Sparql
SELECT ?node ?title WHERE{ ?node <http://purl.org/dc/elements/1.1/title> ?title . } LIMIT 1
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Long! SELECT ?node ?name WHERE{ ?node <http://xmlns.com/foaf/0.1/givenname> ?name . ?node <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person> . } LIMIT 10
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PrefixPREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT ?node ?name WHERE{ ?node foaf:givenname ?name . ?node rdf:type foaf:Person . } LIMIT 10
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Shortcuts PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> SELECT ?node ?name WHERE{ ?node foaf:givenname ?name ; rdf:type foaf:Person . } LIMIT 10
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Graphs
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Named Graph
PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?graph ?node ?title WHERE{ GRAPH ?graph{ ?node dc:title ?title . } } LIMIT 3
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Named GraphPREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?node8 ?desc8 ?node401 ?desc401 WHERE{ GRAPH <http://data-gov.tw.rpi.edu/vocab/Dataset_401>{ ?node401 dc:description ?desc401 . } GRAPH <http://data-gov.tw.rpi.edu/vocab/Dataset_8>{ ?node8 dc:description ?desc8 . } } LIMIT 3
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Union PREFIX dc: <http://purl.org/dc/elements/1.1/> SELECT ?node8 ?desc8 ?node401 ?desc401 WHERE{ { GRAPH <http://data-gov.tw.rpi.edu/vocab/Dataset_401>{ ?node401 dc:description ?desc401 . } }UNION{ GRAPH <http://data-gov.tw.rpi.edu/vocab/Dataset_8>{ ?node8 dc:description ?desc8 . } } } LIMIT 3
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Optional
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?node ?name ?givenname WHERE{ ?node foaf:name ?name . OPTIONAL{ ?node foaf:givenname ?givenname . } }
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Filter
PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?node ?name ?givenname WHERE{ ?node foaf:name ?name . ?node foaf:givenname ?givenname . FILTER regex(?name, "Biden") . }
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Try some on your own
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Questions?