Linking Open Data Linking the world of data from LOD mailinglist Acknowledgement for Tom Heath (Talis) Ying Ding

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

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.

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

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----

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

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

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

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

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: – Book of “Romeo and Juliet”  URL – like a street address

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

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”

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

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

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

Bubble now

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

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?

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) Value (object) Property (predicate) Subject has a property with value “object ” (s,p,o)

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) Value (object) Property (predicate) Literals can be the object of an RDF statement, but cannot be the subject or the predicate

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), , BibTex, Java, Javadoc, etc. to RDF

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

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)

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

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

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

Publish your bubble Step 1: Choosing URIs Reference: Sauermann et al.: Cool URIs for the Semantic Web (tutorial on URI dereferencing and content-negotiation)Cool URIs for the Semantic Web

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: nData/CommonVocabularies  You should only define new terms yourself if you cannot find required terms in existing vocabularies

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

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)

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 owl:sameAs

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.

Test your bubble Step4: test and debug linked data  Vapour linked validation service: a linked data validator (  Use Linked browsers to see whether your information display correctly and your RDF links work Tabulator, Marbles, OpenLink RDF Browser, Disco

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!

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

Document Web vs. Data Web 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?)

More about LOD LOD Wiki  OpenData OpenData Tutorial on how to publish LOD data  Further readings and tools W3C Track LOD WWW2008  Linked Data Planet in New York 2008  LDOW2008 workshop in WWW2008  369/ 369/ ISWC 2008 LOD tutorial  LOD mailinglist