Fusing the Web of Data

Transcription

1 3rd Asian Semantic Web Conference (ASWC 2008) DIST Workshop, Bangkok, Thailand 8 December 2008 Fusing the Web of Data Christian Bizer, Freie Universität Berlin

2 Overview 1. The Web of Data Linked Data Principles Linked Data Deployment Applications that consume Linked Data 2. Linked Data Fusion 1. The Linking Process 2. Inconsistency Resolution 3. Provenance Tracking and Explanations

3 The Classic Web Web Browsers Search Engines Single global information space 1. URLs as globally unique IDs retrieval mechanism 2. HTML as shared content format 3. Hyperlinks HTML hyperlinks HTML HTML Shortcomings Content is not well structured A B C You can not process content within applications You can not ask expressive queries

4 Linked Data Use Semantic Web technologies to 1. publish structured data on the Web, 2. set links between data from one data source to data within other data sources. Thing Thing Thing Thing Thing Thing Thing Thing Thing Thing typed links typed links typed links typed links A B C D E

5 Linked Data Principles 1. Use URIs as names for things. 2. Use HTTP URIs so that people can look up those names. 3. When someone looks up a URI, provide useful RDF information. 4. Include RDF statements t t that t link to other URIs so that t they can discover related things. Tim Berners-Lee /D /Li t

6 The RDF Data Model pd:cygri rdf:type foaf:person foaf:namef Richard Cyganiak foaf:based_near dbpedia:berlin

7 Data objects are identified with HTTP URIs pd:cygri rdf:type foaf:person foaf:namef Richard Cyganiak foaf:based_near dbpedia:berlin pd:cygri = dbpedia:berlin =

8 Dereferencing URIs over the Web pd:cygri rdf:type foaf:person foaf:namef Richard Cyganiak foaf:based_near dbpedia:berlin dp:population skos:subject dp:cities_in_germany i

9 Dereferencing URIs over the Web pd:cygri rdf:type foaf:person foaf:namef Richard Cyganiak foaf:based_near dbpedia:berlin dp:population dbpedia:hamburgdi b skos:subject skos:subject dp:cities_in_germany i dbpedia:muenchen skos:subject

10 The Disco Hyperdata Browser

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12 2. Linked Data Deployment on the Web Is this real? Thing Thing Thing Thing Thing Thing Thing Thing Thing Thing typed links typed links typed links typed links A B C D E

13 W3C Linking Open Data Project Community effort to publish existing open license datasets as Linked Data on the Web interlink things between different data sources

14 LOD Datasets on the Web: May 2007 Over 500 million RDF triples Around 120,000 RDF links between data sources

15 Example RDF Links RDF links from DBpedia to other data sources < owl:sameas < org/ >. < owl:sameas < RDF link from a FOAF profile to DBpedia < foaf:topic_interest <

16 LOD Datasets on the Web: February 2008

17 LOD Datasets on the Web: September 2008 > 2 billion RDF triples > 6 million RDF links

18 The Bio2RDF Project Goals 1. Make bioinformatics data available in RDF format on the Web. 2. Promote the linked data vision within the bioinformatics community. 3. Answer questions which were not possible or practical to ask before. Participants Université Laval, Canada Queensland University of Technology, Australia

19 The Bio2RDF Cloud 27 data sources 260 million records 2,7 billion RDF triples

20 3. Applications What can I do with this? Linked Data Browsers Linked Data Mashups Search Engines Thing Thing Thing Thing Thing Thing Thing Thing Thing Thing typed links typed typed typed links links links A B C D E

21 Linked Data Browsers Tabulator Browser (MIT, USA) Disco Hyperdata Browser (FU Berlin, DE) OpenLink RDF Browser (OpenLink, UK) Zitgist RDF Browser (Zitgist, USA) Humboldt (HP Labs, UK) Fenfire (DERI, Irland) Marbles (FU Berlin, DE)

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23 Linked Data Mashups Domain-specific ifi applications using Linked Data from the Web

24 DBtune Slashfacet Visualizes music-related Linked Data Uses LastFM, MySpace, and BBC data

25 DBpedia Mobile Geospatial entry point into the Web of Data Starts with DBpedia, Revyu and Flickr data

26 DERI Semantic Web Pipes

27 Web of Data Search Engines Falcons (IWS, China) Sindice (DERI, Ireland) MicroSearch (Yahoo, Spain) Watson (Open University, UK) SWSE (DERI, Ireland) Swoogle (UMBC, USA)

28 Falcons

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30 Is this good enough? No.

31 2. Linked Data Fusion Application Integrated View Users want an integrated view on all data that is available about an real-world entity! Data Object 1 Data Object 2 Data Object 3 Data Object 4 owl:sameas Data Object 5 Data Object 6 owl:sameas A B C

32 Linked Data Fusion - Requirements 1. Map data into a single schema so that data can be rendered and queried properly. 2. Smush data from all sources about a single real-world entity while keeping track of information provenance. 3. Resolve inconsistencies in the data by applying different data fusion heuristics. 4. Be able to explain the fusion process Tim Berner-Lee s Oh, yeah? button.

33 Roles in the Linked Data Scenario Data Publisher 1. Publish data itself 2. Set RDF links to other data items describing the same real-world entity. 3. Reuse terms from existing vocabularies or set links to related schemata. 4. Publish metadata about - provenance - timeliness - data license Client Application 1. Map data into single schema. 2. Smush data from different sources about real-world entity. 3. Resolve inconsistencies in the data. 4. Keep track of information provenance and lineage. 5. Explain fusion process.

34 2.1 Setting RDF Links Today: Simple pattern- and graph-matching based techniques used to generate links. Usually proprietary code. There is lots of existing work in database and knowledge representation ti communities on identity resolution to be used. Rule-based approaches Distance-based techniques Probabilistic matching Supervised and unsupervised learning Using a wide range of distance metrics see: Elmagarmid et al: Duplicate Record Detection: ti A Survey. KaDE, 2007.

35 Linking Frameworks Goal: (Semi-)automatically generate RDF Links based on declarative rules. Ongoing work Oktei Hassanzadeh (University of Toronto): ODDLinker Andriy Nikolov et al. (Open University): KnoFuss Julius Volz (Freie Universität Berlin): XXXX CREATE LINKS owl:sameas BETWEEN a FROM dbpedia AND b FROM factbook RESTRICT a TO {?a rdf:type dbpedia-owl:country } METRIC { STRING_SIMILARITY(a/rdfs:label, SIMILARITY( l b/rdfs:label), b l) NUM_SIMILARITY(a/p:populationEstimate, b/factbook:population_total), NUM_SIMILARITY(a/p:areaKm, b/factbook:area_total) total) } THRESHOLDS MATCH 0.9 VERIFY 0.7; seealso: EquivalenceMining

36 Schema Level RDF Links Today: Simple mappings: owl:equivalentclass owl:equivalentproperty rdfs:subclassof rdfs:subpropertyof UMBEL effort: Lots of existing work on schema/ ontology matching to build on. Missing: Agreed-upon way to publish more expressive mapping rules on the Web.

37 2.2 Publish Metadata Document Metadata Dublin Core, Semantic Web Publishing Vocabulary Licensing Metadata Creative Commons Licensing Framework Open Data Commons Public Domain Dedication & Licence (PDDL) # Metadata and Licensing Information < di /d t /Al i rdf:type foaf:document f ; dc:publisher < ; dc:date " "^^xsd:date ; dc:rights < / iki/wp. # The Document Content < rdf:type foaf:person ; foaf:name "Empire, Alec" ; dbpedia-owl:associatedband dbpedia:atari_teenage_riot ;

38 2.3. Provenance and Lineage Tracking Named Graphs data model part of W3C SPARQL Recommendation implemented by an increasing number of RDF stores # TriG Representation of three Named Graphs :G1 { :Monica ex:name "Monica Murphy". :Monica ex:homepage < :Monica ex: <mailto:monica@monicamurphy.org>.} :G2 { :Monica rdf:type ex:person. :Monica ex:hasskill ex:programming } :G3 { :G1 swp:assertedby _:w1. _:w1 swp:authority :Chris. _:w1 dc:date " "^^xsd:date 0 0. :G2 swp:quotedby _:w2. _:w2 swp:authority :Chris. _:w2 dc:date " "^^xsd:date. }

39 2.4. Inconsistency Resolution There is lots of overlap between LOD datasets Places: Dbpedia, Geonames, Riese, People: Freebase, LinkedMDB, DBLP, Music: Dbpedia, Musicbrainz, Jamendo,.. There are naturally lots of inconsistencies Dbpedia: Person born at date X. Freebase: Person born at date Y. Dbpedia: Band album X. Musicbrainz: Band album Y. Geonames: City has geo-coordinates Freebase: City has geo-coordinates

40 Inconsistency Resolution Strategies Pass it on. Pass conflicting values to the user and let him decide. Take the information If value is missing in dataset 1, use value from dataset 2 Trust your friends Prefer information from certain sources. Cry with the wolfes Choose most common value Meet in the middle Take the averadge of all values Keep up to data Use the newest value SeeAlso: Bleiholder and Naumann: Conflict Handling Strategies in an Integrated Information System. WWW2006.

41 2.5. Explain Data Provenance and Fusion Steps Tim Berner-Lee s Oh, yeah? button. Existing Work: Deborah McGuinness et al: Inference Web: Portable Explanations for the Web. Chris Bizer: Web Information Quality Assessment Framework (WIQA)

42 Example WIQA Explanations

43 Outlook Lots of exiting open issues to solve! DIST related technologies will be one of the hot topics for next years (see for instance WWW2009) Important for LOD Progress with Publishing Schema Mappings on the Web Progress with Data Fusion Linked Data client applications that address all issues mentioned Please submit such solutions and client applications to the Semantic Web Challenge 2009 Linked Data on the Web (LDOW2009) workshop at WWW2009 IJSWIS Special Issue on Linked Data

44 Thanks! References Linking Open Data Project Wiki LinkingOpenData Tutorial on How to Publish Linked Data on the Web i /bi / b/li dd t t i l/