Linking Open Data

1. Linking Open Data Linking the world of data from LOD mailinglist Acknowledgement for Tom Heath (Talis) Ying Ding (dingying@indiana.edu) http://info.slis.indiana.edu/~dingying/

2. What is now • User generated content is growing tremendously • Isolated contents need deadly to get connected. • The world is connected, so do the data, information and knowledge

3. Old terms • Data -- sensing the world • What you sense (see, hear, smell, touch…) • Information – perceiving the world • Perceive the sensed data • Knowledge – contextualizing information • Comprehend the perceived information • Add context Context ultimately determines what’s actually what.

4. What is our daily life • Access data • Manipulate data (add, delete, change) • Process data • Generate information (tables, forms) • Create knowledge (reports, papers..)

5. Data is our life • Data is our daily bread • Do we have identifier for data? • Not really important if data is small and individual • Really important if data is huge and connected ? Should we need identifier for our data ? Why do we need our name, or social security number ? Can you refer to someone without identifier ?a person with good heart----

6. Make our busy life less messy • We just got 24 hours per day, not more • Add identifier to our data • Give the everyone-agreed-unique-identifier to each data -- the perfect world of our dreamland • We will not have any integration problem, most of the IT departments can be closed • Different groups give different identifiers to the same data – we can live with that, it is more real in our daily life, standardization bodies and IT guys are helping us. We are happy that we can refer to data

7. Where are our data • In computer • On the Web • In my paper notes • In printed books • … Data are being digitalized and are available online • Web Data

8. Web data • Data on the Web • Online journal • Blog • Wiki • … • Data in physical world • Yourself • Table • Book in library • Computer you are using • … • The boundary is blurring • Paper is both in your hand and on the Web

9. How to refer data • Web data • DOI (Digital Object Identifier) • OpenID (people, …) • URI (blog, wiki, homepage, …) • …

10. URI (Uniform Resource Identifier) • To identify or name a resource on the Internet • The main purpose is to enable interaction with representations of the resource over a network, typically WWW, using specific protocols –from Wikipedia • URN – like a person’s name • urn:isbn:0-486-27557-4 – Book of “Romeo and Juliet” • URL – like a street address • http://www.slis.indiana.edu

11. Linked Data • A term coined by Tim Berners-Lee • It describes HTTP-based Data Access by Reference for the Web • Current web is changing from hypertext links (link documents) to hyperdata links (linking data) • Data are small components of the resources • It drills deep to the details of the resources • Linked data provides a powerful mechanism for meshing disparate and heterogeneous data

12. Vision from Sir Berners-Lee • “The Semantic Web isn’t just about putting data on the web. It is about making links”. • Four Rules for linking data • Use URIs as names for things • Use HTTP URIs so that people can look up those names • When someone looks up a URI, provide useful information (URI dereferencing) • Include links to other URIs, so that they can discover more things • “Breaking them does not destroy anything, but misses an opportunity to make data interconnected. This in turn limits the ways it can later be reused in unexpected ways. It is the unexpected re-use of information which is the value added by the web”

13. W3C SWEO Linking Open Data Project • Project aims to • Publish existing open license datasets as linked data on the web • Interlink things between different data sources • Develop clients and applications that consume linked data from the web

14. Bubbles in May 2007 Over 500M RDF triples Around 120K RDF links between data sources

15. Bubbles in April 2008 >2B RDF triples Around 3M RDF links

16. Bubble now

17. Organization participating in the LOD community • Academic • MIT, Univ Southampton, DERI, Open Univ, Univ London, Univ Hannover, Penn State Univ, Univ Leipzig, Univ Karlsruhe, Joanneum (AT), Free Univ Berlin, Cyc, SouthEast Univ (CN), … • Commercial • BBC, OpenLink, Talis, Zitgist, Garlik, Mondeca, Renault, Boad Interactive

18. What are Linked Data? • Linked Data require RDF • Why not XML? • Different model theory • But not all RDF data are linked data • You have to compliant your RDF data according to the four rules mentioned by Berners-Lee • What is RDF?

19. Basic Ideas behind RDF • RDF uses Web identifiers (URIs) to identify resources • RDF describes resources with properties and property values • Everything can be represented as triples • The essence of RDF is the (s,p,o) triple Resource (subject) Property (predicate) Value (object) Subject has a property with value “object ” (s,p,o)

20. RDF Triples • Triple • A Resource (Subject) is anything that can have a URI: URIs or blank nodes • A Property (Predicate) is one of the features of the Resource: URIs • A Property value (Object) is the value of a Property, which can be literal or another resource: URIs, literal, blank nodes Resource (subject) Property (predicate) Value (object) Literals can be the object of an RDF statement, but cannot be the subject or the predicate

21. Do you have linked data • Linked data are just RDF triples • How can I get RDF triples • Relational database: • D2R tools can convert them for you • RDFizers from SIMILE: • Can convert JPEG, MARC/MODS, OAI-PMH, OCW(MIT Open Course), Email, BibTex, Java, Javadoc, etc. to RDF <rdf:Description about=“http://example.org/smith#albert”> <fam:hasChild rdf:Resource="http://example.org/smith#brian">  <fam:hasChild rdf:Resource="http://example.org/smith#carol"></rdf:Description>

22. Thumb of the rules • Understand your data • What do you want to have in your data • Do not reinvent – REUSE! • Potential ontologies/vocabularies • FOAF, SIOC, Geo • URI Aliases • Different URIs for the same non-information resource (Berlin, etc.) • owl:sameAs to link these URI aliases

23. More principles • Linked Data is simply about using the Web to create typed links between data from different sources. • The principle of Linked data is to: • Use the RDF data model to publish structured data on the web • Use RDF links to interlink data from different data sources. • Use HTTP URIs to identify resource • To avoid other URI schemes (URNs or DOIs)

24. Power of Linked Data rdf:type ying foaf:Person dblp:publications foaf:name foaf:publication foaf:knows Ying Ding Stefan 72K foaf:based_near dp:population db:Galway dp:Dublin skos:subject skos:subject dp:Cities_in_Ireland

25. How to become a bubble • Publishing your bubble • Are you ready? • Dereferencing HTTP URIs • Information resources (resources available on the web): • HTTP GET HTTP response code 200 OK • Non-information resources (real-word objects that exist outside of the web): • HTTP GET HTTP 303 See Other (303 redirect) • You are not your homepage, but you can be dereferenced by your homepage

26. Publish your bubble • Step 1: Choosing URIs • Use HTTP URIs for everything (http://) • Make it dereferenable • Try to use the existing dereferencable URIs to represent common things (city, music, artist, etc.): http://esw.w3.org/topic/TaskForces/CommunityProjects/LinkingOpenData/CommonVocabularies • For instance: Geonames, DBpedia, Musicbrainz, dbtune, RDF Book Mashup • Keep implementation info out of your URIs • Keep your URIs stable and persistent

27. Publish your bubble • Step 1: Choosing URIs http://dbpedia.org/resource/Berlin http://dbpedia.org/page/Berlin http://dbpedia.org/data/Berlin http://id.dbpedia.org/Berlin http://pages.dbpedia.org/Berlin http://data.dbpedia.org/Berlin http://dbpedia.org/Berlin http://dbpedia.org/Berlin.html http://dbpedia.org/Berlin.rdf Reference: Sauermann et al.: Cool URIs for the Semantic Web (tutorial on URI dereferencing and content-negotiation)

28. Publish your bubble • Step2: choose the vocabularies to represent information • Reuse terms from well-known vocabularies wherever possible • Friend of a Friend (FOAF) • Dublin Core (DC) • Semantically-Interlinked Online Communities (SIOC) • Description of a Project (DOAP) • Simple Knowledge Organization System (SKOS) • Creative Commons (CC) • More: http://esw.w3.org/topic/TaskForces/CommunityProjects/LinkingOpenData/CommonVocabularies • You should only define new terms yourself if you cannot find required terms in existing vocabularies

29. Publish your bubble • Step2: choose the vocabularies to represent information • If you really have to define your own vocabularies: • Do not define new vocabularies from scratch • Provide for both humans and machines (rdf:comments, rdfs:label) • Make term URIs dereferenceable • Make use of other people’s terms • State all important information explicitly • Do not create over-constrained, brittle models, leave some flexibility for growth

30. Publish your bubble • Step3: Link your bubble with other bubbles • RDF links enable browsers and crawlers to navigate between data sources and to discover additional data. • foaf:knows, foaf:based_near, foaf:topic_interest • owl:sameAs (map different URI aliases)

31. Publish your bubble • Step3: Link your bubble with other bubbles • Auto-generating RDF Links: • ISBN for books (e.g., RDF Book Mashup) • More complex property-based algorithms • Interlinking DBpedia and Geonames • Interlinking Jamendo and MusicBrainz <http://dbpedia.org/resource/Harry_Potter_and_the_Half-Blood_Prince> owl:sameAs <http://www4.wiwiss.fu-berlin.de/bookmashup/books/0747581088>

32. Publish your bubble • Recipes for publishing different information as Linked Data on the Web • Things must be identified with dereferenceable HTTP URIs • If such a URI is dereferenced asking for the MIME-type application/rdf+xml, a data source must return an RDF/XML description of the identified resource • URIs that identify non-information resources should return HTTP 303 redirect • Besides RDF links to resources within the same data source, RDF descriptions should also contain other RDF links to link to other resources, so that you can browse the web of data.

33. Test your bubble • Step4: test and debug linked data • Vapour linked validation service: a linked data validator (http://vapour.sourceforge.net/) • Use Linked browsers to see whether your information display correctly and your RDF links work • Tabulator, Marbles, OpenLink RDF Browser, Disco

34. Welcome to the bubble world • Very excited! • Then what is my contribution and benefit? • Add more data to RDF data • Increase semantic content • … • … • Bring Web to its full potential!

35. What LOD can bring? • It will lift current document web up to a data web • LOD browsers can let you navigate between different data sources by following RDF links. • It can drill down to the lower granularity of the information • allowing you for more fine search on the web • making the question-answer search on the Web possible • meshing up different data through RDF links • Making the built-on-top application easier

36. Document Web Glued by hyperlinks Data are HTML pages Query result is HTML pages, which can not be further processed Data are just interlinked, but not integrated Data access through different APIs Data Web Glued by RDF links Data are RDF triples Query result is RDF triples which can be easily further processed (e.g., web services) Data are interlinked and integrated, and links are typed Data access through a single and standardized access mechanism (maybe it will called in the future LOD API?) Document Web vs. Data Web

37. More about LOD • LOD Wiki • http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData • Tutorial on how to publish LOD data • http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/ • Further readings and tools • W3C Track LOD WWW2008 • http://www.w3.org/2008/Talks/WWW2008-W3CTrack-LOD.pdf • Linked Data Planet in New York 2008 • http://linkeddata.org/slides/2008-06-nyc-ldp.pdf • LDOW2008 workshop in WWW2008 • http://sunsite.informatik.rwth-aachen.de/Publications/CEUR-WS/Vol-369/ • ISWC 2008 LOD tutorial • http://events.linkeddata.org/iswc2008tutorial • LOD mailinglist