Weaving the Pedantic Web (LD
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Weaving the Pedantic Web (LD

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Weaving the Pedantic Web (LD Weaving the Pedantic Web (LD Presentation Transcript

  • Digital Enterprise Research Institute www.deri.ie Weaving the Pedantic Web LDOW 2010 Aidan Hogan, Andreas Harth, Alexandre Passant, Stefan Decker, Axel Polleres 0:39:00 Copyright 2009 Digital Enterprise Research Institute. All rights reserved. 1
  • Linked Data… Digital Enterprise Research Institute www.deri.ie 2
  • Purpose of talk: Application developers… how to not sink… Digital Enterprise Research Institute www.deri.ie 3
  • Purpose of talk: RDF Publishers… how to avoid common mistakes… Digital Enterprise Research Institute www.deri.ie 4
  • Talking about errors in Linked Data… Digital Enterprise Research Institute www.deri.ie We’ll try not to ruin the party …statistics based on crawl:  April 2009  5k domain limit  150k URIS, 55k RDF docs  12.5m triples (quads)  Mentioning 1.6m URIs  5,850 classes/9,507 props  Accept: application/rdf+xml …okay… so no RDFa Statistics are *illustrative* not exhaustive! 5
  • Digital Enterprise Research Institute www.deri.ie Chapter 1: HTTP-level issues… …a good RDF description these days is hard to find 6
  • Waldo URIs: URIs with no dereferencable RDF Digital Enterprise Research Institute www.deri.ie Not a crawler’s idea of fun… 7
  • Hmm not *so* many… Digital Enterprise Research Institute www.deri.ie  5.3% of HTTP URIs return 40x/50x  Excluding redirects… 92.8% return 200 OK  In return, only 45.4% of 200 Okay return report application/rdf+xml  34.8% return HTML… probably just HTML docs… okay… maybe a *few* contain RDFa 8
  • Lies… Damned Lies… & Content-Type Reporting Digital Enterprise Research Institute www.deri.ie “Trust me, it’s RDF/XML” 9
  • Okay… So he’s actually pretty honest Digital Enterprise Research Institute www.deri.ie  16.9% of valid RDF/XML documents returned with an invalid/more generic Content-type: text/xml (9.5%) application/xml (5.9%) text/plain (1%) text/html (0.4%)  Of those returning Content-type:application/rdf+xml 98.8% were valid RDF/XML 10
  • Same triples, different document Digital Enterprise Research Institute www.deri.ie I wish they’d used a redirect… 11
  • E.g., the Miracle at Calais: turning 1,778 triples into ~∞ quads Digital Enterprise Research Institute www.deri.ie http://d.opencalais.com/1/type/em/r/SameTriplesDifferentDocument (apologies to OpenCalais guys – it’s just a convenient example) 12
  • Digital Enterprise Research Institute www.deri.ie Chapter 2: Reasoning issues… …or, how I learned to start worrying and stop loving OWL 13
  • Undefined classes and properties… Digital Enterprise Research Institute www.deri.ie It looks important, but I’m afraid I don’t fully follow 14
  • Quite common… Digital Enterprise Research Institute www.deri.ie  14.3% of triples use undeclared property  8.1% of triples use undeclared class  Three cases:  Case 1: Namespace has no vocabulary/ is not deferencable (e.g., rss:item)  Case 2: Term invented in related namespace (e.g., foaf:tagLine invented by LiveJournal)  Case 3: Term is misspelt version of term defined in namespace (e.g., foaf:image vs. foaf:img) 15
  • Not-so-unique values for Inverse-Functional Properties Digital Enterprise Research Institute www.deri.ie Despite what you claim, not all of you can *actually be* Spartacus 16
  • Spartacus relived… Digital Enterprise Research Institute www.deri.ie 08445a31a78661b5c746feff39a9db6e4e2cc5cf  sha1-sum of „mailto:‟  common value for foaf:mbox_sha1sum  An inverse-functional (uniquely identifying) property!!!  Any person who shares the same value will be considered the same *I’m Spartacus!* …and so’s my wife 17
  • …unattended, can be pretty serious… Digital Enterprise Research Institute www.deri.ie foaf:mbox_sha1sum a owl:InverseFunctionalProperty . ?x foaf:mbox_sha1sum 08445a31a78661b5c746feff39a9db6e4e2cc5cf . OWL 2 RL rule prp-ifp: ?p a owl:InverseFunctionalProperty . ?x1 ?p ?z . ?x2 ?p ?z . ⇒ ?x1 owl:sameAs ?x2 . 106 ?x1/?x2bindings in body 1012 inferred pair-wise and reflexive owl:sameAs statements …or in simpler terms: pow! 18
  • Malformed/incompatible datatypes Digital Enterprise Research Institute www.deri.ie As he would undoubtedly be able to tell you, “true” is not a valid xsd:int 19
  • Not *too* bad… Digital Enterprise Research Institute www.deri.ie  4.7% of typed literals were “ill-typed” (lexically invalid)…  mostly xsd:dateTimes (26.4% of all date-time literals were invalid; e.g., omitted the seconds field)  Also, literals are sometimes incompatible with the datatype-range of a property:  E.g., 21.8% of ical:description triples used language tags incompatible with the defined range of xsd:string  E.g., 100% of sl:creationDate triples use plain literal values incompatible with defined range of xsd:date 20
  • Mystical beings… Members of disjoint classes Digital Enterprise Research Institute www.deri.ie Despite what FOAF says, it seems that Persons can also be Documents 21
  • Again, not *too* bad… Digital Enterprise Research Institute www.deri.ie  1,329 members of disjoint classes found  Generally caused by naïve URI naming:  Use of information resource URIs to name entities (particularly foaf:Persons)  E.g., <me> foaf:knows <jim/foaf.rdf> . 22
  • Ontology hijacking… Digital Enterprise Research Institute www.deri.ie Anybody can say anything, anywhere, and unfortunately for everyone else, have a good chance of being taken seriously 23
  • Redefining Everything… …and home in time for tea Digital Enterprise Research Institute www.deri.ie From http://www.eiao.net/rdf/1.0 <owl:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#type"> <rdfs:label xml:lang="en">type</rdfs:label> <rdfs:comment xml:lang="en">Type of resource</rdfs:comment> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#testRun"/> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#pageSurvey"/> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#siteSurvey"/> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#scenario"/> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#rangeLocation"/> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#startPointer"/> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#endPointer"/> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#header"/> <rdfs:domain rdf:resource="http://www.eiao.net/rdf/1.0#runs"/> </owl:Property> Ontology hijacking!! (apologies to EIAO guys – it’s just a convenient example) 24
  • Solutions? Digital Enterprise Research Institute www.deri.ie 25
  • Application side: workarounds Digital Enterprise Research Institute www.deri.ie  All presented issues have a suitable antidote, once you know about them  See paper for discussion… 26
  • Publishing side: Validators! Digital Enterprise Research Institute www.deri.ie  Syntax errors quite rare, partly due to popularity of W3C RDF/XML syntax validator  Need an all-in-one validation service  Should not only validate strict errors, but give feedback on suspected issues  We offer a prototypical service at: http://swse.deri.org/RDFAlerts/ 27
  • Publishing side: Pedantic Web Group Digital Enterprise Research Institute www.deri.ie  Get the community to contact publishers about errors/issues as they arise  Get involved: http://pedantic-web.org/  137 members!  Acknowledgements to: Aidan Hogan, Alex Passant, Me, Antoine Zimmermann, Axel Polleres, Michael Hausenblas, Richard Cyganiak, Stéphane Corlosquet 28