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The Semantic Web in ActionKennissystemen, November 2009
Rinke Hoekstra
Overview
• The Semantic Web– Languages and Integration– Storage and Querying
• Linked (Open) Data– Scalability issues– Browsing and Viewing
• DEMOs• … if there’s time …
– OWL in Action04/10/2023 2
The Semantic Web Ideology
• Identity is everything• Partial solutions are great too!• Layer cake
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OWL
Semantic Web
• Intially• `Metadata’ for web pages
• Since ~2006• `Web of Data’• Semantic web as data source in its own right
• Linked Data
• A ‘Databaseesque’ Web• RDF Triple stores• Query languages
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Languages
• Multiple Languages– RDF, RDFS and OWL
• Multiple Syntaxes– RDF/XML, Turtle (Restricted N3), Ntriple– Functional Syntax, Manchester Syntax, OWL XML
• RDF– Triples <subject, predicate,object>– Distributed– Always about something else– ... but can be about other RDF triples as well.
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Languages: RDF(S)/XML<rdf:RDF xmlns:rdf=“http://www.w3.org/1999/02/22-rdf-syntax-ns#” xmlns:rdfs="http://www.w3.org/TR/rdf-schema/" xmlns:owl=“http://www.w3.org/2002/07/owl#” xmlns:uva=“http://www.uva.nl/rdf#” xmlns=“http://www.uva.nl/people”> <rdf:Description rdf:ID=“#radboud”> <rdf:type rdf:resource=“http://www.uva.nl/rdf#AssociateProfessor”/> <uva:name>Radboud Winkels</uva:name> <uva:teaches rdf:resource=“http://www.uva.nl/courses#ks2009”/> </rdf:Description> <uva:Course rdf:about=“http://www.uva.nl/courses#ks2009”/> <rdfs:Class rdf:about=“http://www.uva.nl/rdf#AssociateProfessor”> <rdfs:subClassOf rdf:resource=“http://www.uva.nl/rdf#StaffMember”/> </rdfs:Class> <owl:ObjectProperty rdf:about=“http://www.uva.nl/rdf#teaches”> <rdfs:domain rdf:resource=“http://www.uva.nl/rdf#Professor”/> <rdfs:range rdf:resource=“http://www.uva.nl/rdf#Course”/> </owl:ObjectProperty></rdf:RDF>
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Languages: Turtle@prefix rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>.@prefix rdfs:<http://www.w3.org/TR/rdf-schema/>.@prefix owl:<http://www.w3.org/2002/07/owl#>.@prefix uva:<http://www.uva.nl/rdf#>.@prefix courses:<http://www.uva.nl/courses#>.@prefix :<http://www.uva.nl/people#>.
uva:AssociateProfessor a rdfs:Class;rdfs:subClassOf uva:StaffMember.
uva:teaches a owl:ObjectProperty;rdfs:domain uva:AssociateProfessor;rdfs:range uva:Course.
:radboud a uva:AssociateProfessor;uva:name ”Radboud Winkels”^^xsd:string;uva:teaches courses:ks2009.
courses:ks2009 a uva:Course.
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Languages: FS
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Namespace(=<http://www.uva.nl/people#>)Namespace(owl=<http://www.w3.org/2002/07/owl#>)Namespace(uva=<http://www.uva.nl/rdf#>)Namespace(courses=<http://www.uva.nl/courses#>)
Declaration(Class(uva:Course))Declaration(Class(uva:StaffMember))Declaration(Class(uva:AssociateProfessor))SubClassOf(uva:AssociateProfessor uva:StaffMember)
Declaration(DataProperty(uva:name))Declaration(ObjectProperty(uva:teaches))ObjectPropertyDomain(uva:teaches uva:AssociateProfessor)ObjectPropertyRange(uva2:teaches uva:Course)
Declaration(Individual(courses:ks2009))Declaration(Individual(radboud))ObjectPropertyAssertion(uva:teaches radboud courses:ks2009)DataPropertyAssertion(uva:name radboud "Radboud Winkels")
Integration
• How to add this ‘meta’ to my ‘data’?• Three options:
– Old fashioned HTML:<link rel='meta' type='application/rdf+xml' href='http://www.leibnizcenter.org/~hoekstra/foaf.rdf' title='FOAF'>
– HTTP 303 `see other’http://www.w3.org/TR/swbp-vocab-pub/
– Inline (RDFa/GRDDL)
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Integration: 303 See Other (Demo)http://www.metalex.eu/metalex
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Integration: Inline
• RDFa– Attributes on XHTML elements– http://www.w3.org/TR/xhtml-rdfa-primer
• GRDDL– Gleaning Resource Descriptions from Dialects of
Languages– Explicit reference to (XSL) transformation– http://www.w3.org/TR/grddl/
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Integration: RDFa Example• In XHTML:<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd"><html xmlns:cal="http://www.w3.org/2002/12/cal/ical#"> <head><title>Jo's Friends and Family Blog</title></head> <body> <p instanceof="cal:Vevent"> I'm holding <span property="cal:summary">one last summer Barbecue</span>, on <span property="cal:dtstart" content="20070916T1600-0500"> September 16th at 4pm. </span> </p> </body></html>
• In RDF:_:blanknode0 rdf:type cal:Vevent; cal:summary ”one last summer Barbecue"; cal:dtstart "20070916T1600-0500" .
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Integration: GRDDL• In HTML/XML instance documents:<html xmlns="http://www.w3.org/1999/xhtml" xmlns:grddl='http://www.w3.org/2003/g/data-view#' grddl:transformation="glean_title.xsl
http://www.w3.org/2001/sw/grddl-wg/td/getAuthor.xsl”>
• In XML Schema documents: <xsd:annotation> <xsd:appinfo> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about="http://www.metalex.eu/latest"> <grddl:namespaceTransformation rdf:resource=”http://www.metalex.eu/grddl/metalex2owl.xsl" /></rdf:Description>
</rdf:RDF> </xsd:appinfo> </xsd:annotation>
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Storage (on the web)
• As documents– .rdf, .n3, .turtle, .html
• RDF triple stores– Sesame, Joseki, 4Store, AllegroGraph, OpenLink
Virtuoso, SDB/TDB, Open Calais, SWI Prolog – Reasoners ‘on top’, or via DIG
• Pellet, OWLIM, etc.
• SPARQL Endpoints– Results as JSON, XML, CSV etc.
04/10/2023 14
Querying
• Originally many languages– SPARQL, nRQL, SeRQL, etc.
• SPARQL: – http://www.w3.org/TR/rdf-sparql-query/
• ExamplePREFIX course: <http://www.uva.nl/courses#>PREFIX uva: <http://www.uva.nl/rdf#>SELECT ?nameWHERE { ?x uva:teaches course:ks2007. ?x uva:name ?name }
?x binds with <http://www.uva.nl/people#radboud> ?name binds with “Radboud Winkels”^^xsd:string
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Querying (2)
• SPARQL 1.0– select, construct, from, optional, filter– Negation via unbound variable
• SPARQL 1.1– update, negation, aggregation, subqueries
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04/10/2023 19November 2009: 13.1 Billion triples, 142 Million links
But there’s more
• Late additions…– New York Times archives
• Now 5k names, with 4 references to LOD• Will grow to > 30k
– Reuters– OpenCalais automated tagging
• Soon to come– Data.gov (via RPI)– Whitehouse.gov (via Drupal)– Data.gov.uk (directly)– European Parliament (MetaLex+RDFa)
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Scalability
• How to deal with massive amounts of data?
• Consequences for reasoning– Billion Triple Challenge– (864.8 Million Triples)
• Consequences for querying– Table lookups, joins etc.
• … and what about …– Dealing with change, provenance, trust?
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A rough idea…
• I can crash a DL reasoner using an ontology of ~15 classes and 5 individuals (honestly)
• What if my ontology contains thousands of classes and billions of individuals?
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Reasoning• When?
– Realtime vs. in advance
• Lightweight reasoning (RDFS, OWL 2 RL)– Implementable using forward chaining rules– Still problems with scalability
• Distributed reasoning (DAS-3)– MaRVIN
• ‘SpeedDate’ distrubution of triples across nodes
– MapReduce• Full closure of BTC in 57 minutes• Output: 30B triples
• And what to do with the results?
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2 Degrees from Kevin BaconPREFIX p: http://dbpedia.org/property/SELECT ?film1 ?actor1 ?film2 ?actor2WHERE {
?film1 p:starring <http://dbpedia.org/resource/Kevin_Bacon> . ?film1 p:starring ?actor1 . ?film2 p:starring ?actor1 . ?film2 p:starring ?actor2 .}
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DBPedia: 150M triples
Rough idea…
• 1 Billion triples in MySQL– Load time
• … a couple of hours
– Simple table lookup (one-variable query)• … about 5 minutes
– Single join (two-variable query)• … a couple of hours
• Better indexes?– Harddisk access times are the bottleneck (9ms)
• More targeted reasoning, querying, federation.
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LET’S SUPPOSE THAT ALL WORKSViewing the web of data
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Browsing and Viewing
• How to unlock your RDF/OWL to users?– Custom applications (PizzaFinder)– Generic RDF Browsers (Faceted Browsing)
• How to present your RDF/OWL to users?– Custom applications (TopBraid Geo)– Generic RDF Visualisation (Fresnel Lenses)
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Browsing: Facets• Multi-dimensional search• User filters available information• Context dependent• Facet
– UI element– Values of a property– Number of results
• Query building
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Browsing• MIT Longwell
– http://simile.mit.edu/longwell/demo/libraries• /facet
– http://slashfacet.semanticweb.org• Flamenco• RDFBrowser• Exhibit
– http://simile.mit.edu/exhibit• LENA• OpenAcademia
– http://vu.openacademia.org
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Viewing
• Tables are boring!• Different data? Different presentation:
– URI/URL– Images– Strings– Coordinates
• Filtering data• Aggregating data
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Viewing: Fresnel
• RDF specification of– What data to present, and– How to present it
• http://www.w3.org/2005/04/fresnel-info
• Lenses– Group information
(class membership, SPARQL result)• Formats
– Specify how property values should be rendered04/10/2023 31
Viewing: Fresnel lens:foafPersonDefaultLens rdf:type fresnel:Lens ; fresnel:purpose fresnel:defaultLens ; fresnel:classLensDomain foaf:Person ; fresnel:group :foafGroup ; fresnel:showProperties ( foaf:name foaf:surname foaf:depiction ) .
:knowsLens rdf:type fresnel:Lens ; fresnel:classLensDomain foaf:Person ; fresnel:group :foafGroup ; fresnel:showProperties ( foaf:name foaf:surname foaf:mbox [ rdf:type fresnel:PropertyDescription ; fresnel:property foaf:knows ; fresnel:sublens :foafPersonDefaultLens ] ) .
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Viewing: Fresnel format:foafGroup rdf:type fresnel:Group ; fresnel:stylesheetLink <http://www.example.org/example.css> .
:depictFormat rdf:type fresnel:Format ; fresnel:propertyFormatDomain foaf:depiction ; fresnel:label fresnel:none ; fresnel:value fresnel:image ; fresnel:valueStyle "imageWithThickBorder"^^fresnel:styleClass ; fresnel:group :foafGroup .
:urlFormat rdf:type fresnel:Format ; fresnel:propertyFormatDomain foaf:homepage ; fresnel:propertyFormatDomain foaf:mbox ; fresnel:value fresnel:externalLink ; fresnel:labelStyle "basicLabel"^^fresnel:styleClass ; fresnel:valueStyle "basicUrl"^^fresnel:styleClass ; fresnel:group :foafGroup .
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OWL in Action
• What OWL can do…• Traditional
– Straightforward classification tasks• Extensions
– Explanation & Justification– Probabilistic Reasoning
• Advanced (Law)– Temporal reasoning (Klarman et al., 2008)– Legal reasoning (van de Ven et al., 2008)
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Legal assessment• Case input
– Individual case description• Match
– Case is matched against a set of norms• Resolve conflicts
– Where multiple norms apply, the system determines whether and which norms have priority over others
• Final verdict
University library regulationsNorms qualify a situation
1a) Students registered at this university are allowed to check out a book from this library
1b) Students registered at other universities are allowed to check out a book from this library provided that they are enrolled in at least one course given at this university.
1c) Students who have checked out more than five books are not allowed to check out another book.
Expected subsumption hierarchy:• Art1c ⊑ Art1a, Art1c ⊑ Art1b
AmyC {Amy :Student, book_1 :Library_Book, … , book_6 :Library_BookAmy checks_out book_1, … , Amy checks_out book_6}
A Default Norm0) Default: Checking out books is disallowed.
Default_GC⊑ Generic_Case⊑ ∃disallowed_by.{defaultnorm}≡ ∃checks_out.Library_Book
Default_Norm
⊑ Prohibition ⊑ ∀disallows.Default_GC≡ {defaultnorm}
Article 1a1a) Students registered at this university are allowed to
check out a book from this library.
Art1a_GC⊑ Generic_Case⊑ ∃allowed_by.art1a≡ Registered_Student ⊓
∃checks_out.Library_Book Art1a_Permission
⊑ Permission⊑ ∀allows.Art1a_GC≡ {art1a}
Article 1c1c) Students who have checked out more than five books are not
allowed to check out another book.
Art1c_GC_F⊑ Generic_Case⊑ ∃disallowed_by.{art1c}≡ Registered_Student ⊓ ≥ 6 checks_out.Library_Book
Art1c_GC_P⊑ Generic_Case⊑ ∃allowed_by.{art1c}≡ Registered_Student ⊓
∃checks_out.Library_Book≤ 5 checks_out.Library_Book
Art1c_Prohibition ⊑ Prohibition⊑ ∀disallows.Art1c_GC_F ⊓ ∀allows.Art1c_GC_P ≡ {art1c}
Resources
• http://www.w3.orgRDF(S), N3, OWL, SPARQL, RDFa, GRDDL, XML, XMLSchema, XSLT, CSS, XPath, fresnel...
• http://www.semanticweb.org/facet, other resources
• http://www.planetrdf.comAggregated RSS feed of the cool & famous
• NEW: OWL 2– http://www.w3.org/TR/owl-overview
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