SAMT09 - Web of Data Tutorial - Part 1

1 SAMT 2009 – Tutorial Web of Data in the Context of Multimedia (WoDMM) Graz, Austria - 2 Dec 2009

Web of Data in the Context of Multimedia Part 1: Linked Open Data: Vision, Concepts and Technologies

Bernhard Haslhofer, Bernhard Schandl, Andreas Langegger,

Wolfgang Halb, Tobias Bürger


Agenda   Introduction

  Producing Linked Data

  Existing Data Sets

  Linking Data

  Consuming Linked Data

  Multimedia Interlinking

  Multimedia Annotations

  Enriching Personal Media Collections


Introduction: The Web of Data Vision






  There is lots of data about the movie “The Shining” available on the Web…

Web of Data Vision

Genre: Horror/Thriller

Title: The Shining

Release Date: 23 May 1980 (USA)

Distributors: Warner Bros. Pictures Distribution

Starring: Jack Nicholson, Shelly Duvall, Danny Lloyd, …

Produced by: Stanley Kubrick

Running Time: 146 min (original), 144 min (cut), 120min (European cut)


Web of Data Vision   …but only in a human-readable representation

(HTML)

  Difficult to access these data by applications, unless   they start parsing HTML representations (difficult, erroneous)

  they use data source specific APIs (e.g., Web Services), if there are any

  Metadata about (multimedia) resources are still locked in closed data silos


DB DB

DB DB


Web of Data Vision   The Web is successful because it provides

  Uniform encoding (HTML)

  Uniform addressing (URI)   Uniform transportation (HTTP)

for the exchange of documents.

  Why not apply the same mechanism to the underlying data?


Web of Data Vision

  The Web of Data vision is to use the Web to provide access not only to documents but also to the underlying data


The Linked Data Principles

  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, using the standards (RDF, SPARQL)

  Include links to other URIs, so that they can discover more things


The Enabling Technologies


URI   Uniform Resource Identifiers (URI) identify things

  Use dereferencable HTTP URIs in the Web of Data


RDF   A data model for representing metadata on the Web

  Several statements (triples) form a graph


RDF   Links are an intrinsic RDF feature


RDF/XML, N3, Turtle, etc


RDFS   A language for describing vocabularies in a machine-

understandable way


OWL   A more expressive language for expressing

vocabularies and/or ontologies in a machine-understandable way


SKOS   A language for describing controlled vocabularies


SPARQL   A query language and protocol for accessing RDF

data on the Web


Linked Data Implementation Best Practices


How to publish vocabularies

  Hash-based URIs   E.g., http://example.com/example1#ClassA

  Suited to group the description of a moderate number of related terms into one document

  Agent can retrieve terms with a single HTTP request

  Slash-based URIs   E.g., http://example.com/example1/ClassB

  Suited to split the descriptions of terms in large vocabularies into one document per term

  No need for the agent to download a massive document to find the description of a term


How to publish vocabularies E.g.. extended configuration for hash namespace


How to publish vocabularies E.g.. extended configuration for hash namespace


How to publish Linked Data   Distinguish between

  non-information resource   http://dbpedia.org/resource/The_Shining_%28film%29

  Information resource   http://dbpedia.org/page/The_Shining_%28film%29 (HTML)

  http://dbpedia.org/data/The_Shining_%28film%29 (RDF)


The Linking Open Data Project


Some clarifications   Open Data: a philosophy, practice, or policy that data

are freely available to everyone without restrictions from copyright, patents, a.s.o.

  Linked Data: best practices for exposing, sharing, and connecting data using URIs and RDF

  Linking Open Data: a W3C community project with the goal to extend the Web with a data commons by publishing various open data sets as RDF on the Web and by setting links between data items from different sources


As of October 2007




Available Tools - Overview


RDF APIs   Jena Semantic Web Framework (Java)

  http://jena.sourceforge.net/

  Sesame

  ARC (PhP)   http://arc.semsol.org/

  Redland RDF – Ruby interface (Ruby)   http://librdf.org/docs/ruby.html

  RDFlib (Python)   http://www.rdflib.net/


Triple Stores   Jena Semantic Web Framework (Java)

  http://jena.sourceforge.net

  Sesame (Java)   http://www.openrdf.org/

  OpenLink Virtuoso   http://virtuoso.openlinksw.com/dataspace/dav/wiki/Main/

  ARC (PhP)   http://arc.semsol.org/

  …


References   RDF Primer: http://www.w3.org/TR/rdf-primer/

  OWL 2 Overview: http://www.w3.org/TR/2009/REC-owl2-primer-20091027/

  Best Practice Recipes for Publishing RDF Vocabularies: http://www.w3.org/TR/swbp-vocab-pub/

  How to Publish Linked Data on the Web: http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/

  Pedantic Web Group: http://pedantic-web.org/


References   Linking Open Data Project

  http://esw.w3.org/topic/SweoIG/TaskForces/CommunityProjects/LinkingOpenData

38 SAMT 2009 – Tutorial Web of Data in the Context of Multimedia (WoDMM) Graz, Austria - 2 Dec 2009 38 SAMT 2009 – Tutorial Web of Data in the Context of Multimedia (WoDMM) Graz, Austria - 2 Dec 2009




  Linking Data






Linked Data Publishing Steps The basic tenets of Linked Data are to:

  use the RDF data model to publish structured data on the Web

  use RDF links to interlink data from different data sources

RDF data can be contained in

  a single file (RDF/XML) or

  embedded in an existing file with RDFa


Principles   Resources

all items of interest are called resources

  Resource Identifiers Uniform Resource Identifiers (URIs) are used, use of HTTP URIs is strongly suggested

  Representation of an information resource is a stream of bytes (HTML, JPG, RDF, …)

  Dereferencing HTTP URIs


Content Negotiation Example:   http://dbpedia.org/resource/Graz

(URI identifying the non-information resource Graz)

  http://dbpedia.org/data/Graz (information resource with an RDF/XML representation describing Graz)

  http://dbpedia.org/page/Graz (information resource with an HTML representation describing Graz)


Content Negotiation with RDFa   When RDF is embedded in another representation

(e.g. via RDFa) no content negotiation is needed

  One representation is used for both humans and machines

(X)HTML

RDF

XHTML+RDFa representation


RDFa example Plain (X)HTML: ... All content on this site is licensed under

<a href="http://creativecommons.org/licenses/by/3.0/"> a Creative Commons License </a>.

(X)HTML with RDF embedded: ... All content on this site is licensed under

<a rel="license“ href="http://creativecommons.org/licenses/by/3.0/"> a Creative Commons License </a>.

More information on RDFa:

http://www.w3.org/TR/xhtml-rdfa-primer/


Choosing URIs   Resources are named with URI references

  Choose „good“ URIs for your resources

  Cool URIs for the Semantic Web http://www.w3.org/TR/cooluris/


Choosing URIs   Use HTTP URIs for everything

  Define your URIs in an HTTP namespace under your control

  Keep implementation details out of your URIs. Short, mnemonic names are better   http://dbpedia.org/resource/Graz VS

  http://www.confuseme.com:2020/demos/xyz/cgi-bin/resources.php?id=Graz

  Try to keep your URIs stable and persistent Cool URIs don’t change!

  Use some kind of primary key inside your URIs (e.g. when dealing with books use the ISBN, etc.)


Which vocabularies to use?   Reuse terms from well-known vocabularies wherever

possible

  Only define new terms yourself if you can’t find required terms in existing vocabularies

  List of well-known vocabularies: http://esw.w3.org/topic/TaskForces/Community Projects/LinkingOpenData/CommonVocabularies


Some well-known vocabularies   Friend-of-a-Friend (FOAF), vocabulary for describing

people.   Dublin Core (DC) defines general metadata attributes.   Semantically-Interlinked Online Communities (SIOC),

vocabulary for representing online communities.   Description of a Project (DOAP), vocabulary for describing

projects.   Simple Knowledge Organization System (SKOS),

vocabulary for representing taxonomies and loosely structured knowledge.

  Music Ontology provides terms for describing artists, albums and tracks.

  Review Vocabulary, vocabulary for representing reviews.   Creative Commons (CC), vocabulary for describing

license terms.


More best practices   You can mix terms from different vocabularies, e.g.

rdfs:label and foaf:depiction

  Use URI references from well-established data sources, e.g.:   Geonames

  DBpedia

  MusicBrainz

  RDF Book Mashup


Defining your own terms If you need to define own terms use RDFS or OWL.

1. Do not define new vocabularies from scratch

2. Provide for both humans and machines

3. Make term URIs dereferenceable

4. Make use of other people's terms

5. State all important information explicitly

6. Do not create over-constrained, brittle models; leave some flexibility for growth


What should the RDF contain? What triples should go into the RDF representation that

is returned (after a 303 redirect) in response to dereferencing a URI identifying a non-information resource?

  Description

  Backlinks

  (Related descriptions)

  Metadata

  Syntax: RDF/XML (+ maybe other serializations)


Serving linked data   Things must be identified with dereferenceable HTTP

URIs

  When MIME-type application/rdf+xml is requested, a data source must return an RDF/XML description of the identified resource

  Provide RDF links to other resources so that clients can navigate the Web of Data by following RDF links


Serving static RDF files   RDF files generated manually or

  generated by some software

  Configure server for correct MIME types   When using Apache and server is not yet configured to return the

correct MIME type add to httpd.conf or .htaccess: AddType application/rdf+xml .rdf

  File size (should be < 1 MB)


Serving relational databases   Several tools exist to generate RDF from relational

databases


Linked Data Publishing Steps For more information:

  Tutorial „How to Publish Linked Data on the Web”   By Chris Bizer, Richard Cyganiak, Tom Heath

  http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/


RDB2RDF   W3C Incubator Group in 2008 & early 2009 to

examine existing approaches for generating RDF from relational databases http://www.w3.org/2005/Incubator/rdb2rdf/

  Survey of Current Approaches for Mapping of Relational Databases to RDF http://www.w3.org/2005/Incubator/rdb2rdf/RDB2RDF_SurveyReport.pdf

  Incubator Group Report http://www.w3.org/2005/Incubator/rdb2rdf/XGR-rdb2rdf/


RDB2RDF Working Group   W3C Working Group started in 2009 to standardize

a language for mapping relational data and relational database schemas into RDF and OWL, tentatively called the RDB2RDF Mapping Language, R2RML http://www.w3.org/2001/sw/rdb2rdf/

  First public results to be expected in early 2010

  Participants from industry and academia


Tools for Publishing Linked Data


Pubby Linked Data Frontend   Provides Linked Data from SPARQL endpoint

  data must be available in RDF already

  if not: use a wrapper

  Originally developed for DBpedia   Richard Cyganiak, Chris Bizer - FU Berlin

  Provides dereferenceable HTTP-URIs

  Simple HTML interface for browsing

  Handles 303 redirects correctly

  Content Negotiation (HTML, RDF/XML, N3)

  Java Web application


Pubby - Architecture

  SPARQL endpoint must support DESCRIBE queries

  supports multiple datasets (SPARQL endpoints)

Text

Text


Pubby Setup How-To   Download and extract from:

http://www4.wiwiss.fu-berlin.de/pubby/download

  Setup a Servlet Container (e.g. Tomcat, Jetty...)

  Use ant to build WAR or copy /webapp folder

  Configure   config file in WEB-INF/config.n3   file location can be set by context param. “config-file” in web.xml

  N3 syntax

  General Server section (instance of conf:Configuration)   conf:webBase - root of URL of web application, e.g. http://localhost/

  sub-section for each dataset   conf:sparqlEndpoint - SPARQL endpoint URI

  conf:datasetBase - common URI prefix of resources in the dataset


Wrapping Relational Databases   D2RQ-Map and D2R-Server (FU Berlin)

  http://sites.wiwiss.fu-berlin.de/suhl/bizer/d2r-server/index.html)

  Triplify (Uni Leipzig)   http://triplify.org)

  OpenLink Virtuoso RDF Views   http://virtuoso.openlinksw.com/wiki/main/Main/


D2RQ-Map and D2R-Server   Java

  wraps any ODBC database to RDF

  2 Components   D2RQ-Map (wrapping component): dumps + virtual

  D2R-Server (adds SPARQL endpoint)

  can be used in Jena applications (Assembler)

  Automatic generation of mapping file (simple)   shell script: “generate-mapping”


D2RQ-Map and D2R-Server


D2R-Server How-To   Download/Extract

  Generate mapping file automatically first   generate-mapping -o mapping.n3 -d driver.class.name!

-u db-user -p db-password jdbc:url:..."  Inspect the generated mapping   Model your desired target graph

  you should always know what you want...

  also study your source database model

  Adjust the mapping


Mapping language   d2rq:Database

  d2rq:ClassMap

  d2rq:PropertyBridge

  Rather expressive   Joins

  Conditions

  Value-translations


Example Mapping


Wrapping Spreadsheets   Excel2RDF, RDF123, TopBraid Composer

  XLWrap (A. Langegger)   http://xlwrap.sourceforge.net/

  supports cross tables, repetitive patterns in spreadsheets

  arbitrary target graphs   powerful expressions (extensible, user-defined functions)


XLWrap Example


Example Template Graph §  [ xl:uri "'http://example.org/revenue_' &!§  URLENCODE(SHEETNAME(A1) & '_' & B2 & '_' &!§  A4)"^^xl:Expr ] a ex:Revenue ;!§  ex:country "DBP_LOCALITY(SHEETNAME(A1))"^^xl:Expr ;!§  ex:year "DBP_YEAR(B2)"^^xl:Expr ;!§  ex:product "A4"^^xl:Expr ;!

§  ex:itemsSold "B4"^^xl:Expr ;!§  ex:revenue "C4"^^xl:Expr .!

Text





  Linking Data






Existing Relevant Linked Data Sets

What is out there?


The Linked Data Cloud

(a success story, 2007-2009)


74 SAMT 2009 – Tutorial Web of Data in the Context of Multimedia (WoDMM) Graz, Austria - 2 Dec 2009 10/2007

75 SAMT 2009 – Tutorial Web of Data in the Context of Multimedia (WoDMM) Graz, Austria - 2 Dec 2009 03/2008





Some numbers Data Set # of RDF Triples

ACM RKB > 12,000,000

AudioScrobbler > 600,000,000

BBC Music + Programmes > 20,000,000

Bio2RDF > 2,000,000,000

data.gov > 5,000,000,000

DBpedia > 470,000,000

Freebase > 100,000,000

Geonames > 90,000,000

Linked Geo Data > 3,000,000,000

MusicBrainz > 60,000,000

RDF Book Mashup > 100,000,000

US Census Data > 1,000,000,000 Source: http://esw.w3.org/topic/TaskForces/CommunityProjects/LinkingOpenData/DataSets/Statistics


DBpedia: the Linked Data Hub   DBpedia [Auer07] is a Linked Data representation of

Wikipedia content.

  (Semi-)structured data are extracted (mostly from infoboxes) and are published as RDF.

  DBpedia 3.4 (Nov. 2009) describes 2.9 million things, including persons, places, organizations, ...

  Each thing has an URI; most of them have a label and an abstract, in up to 91 languages.

  DBpedia provides > 8 millions links to other data sets (web pages and RDF), and 75,000 YAGO categories.


DBpedia Vocabularies

  DBpedia uses its own set of terms, which are derived from the naming in Wikipedia Infoboxes.

  Additionally used: RDF standard terms, FOAF.

  The importance of DBpedia lies not primarily in the data it provides, but in the names (i.e., HTTP URIs) it provides.




BBC Linked Data   BBC is continually increasing their Linked Data

services.

  BBC Programmes publishes all broadcast programmes and provides URIs for them.

  BBC Music provides data about music artists and links to DBpedia and MusicBrainz.

  BBC uses Linked Data technology to link their internal, heterogeneous data sets [Kobi09].

  Used vocabularies: RDF(S), FOAF, DC, Music Ontology, ...




DBtune   DBtune [Rai08] is a collection of music-related

Linked Data sets, amongst others:   Jamendo (creative commons music site)

  MusicBrainz (community music metadata)

  AudioScrobbler (last.fm playcounts)

  MySpace

  URIs for entities can be retrieved by lookup services or through links to DBpedia and other data sets.

  Used vocabularies: RDF(S), FOAF, DC, Music Ontology, ...




Linked Movie Data Base   LMDB [Hass09] is an RDF representation of parts of

the data from the Internet Movie Database (IMDb).

  Data about ~40,000 films, ~30,000 actors, ~8,000 directors, etc.

  Links to   DBpedia

  YAGO

  flickr

  RDF book mashup

  MusicBrainz

  Geonames

  Vocabularies: RDF(S), FOAF, Movie Ontology, SKOS, DC




There is more ...   flickr wrapper: generates links to flickr pictures on

demand, represents them as RDF

  Geonames: information about places (cities, countries)

  Linked Geo Data: RDF representation of OpenStreetMap (geo data)

  revyu.com: provides reviews for any kind of entities (including movies and music)

  New York Times: >5.000 concepts from their archive

  and many more ...

  Data is out there ... use it!


References & Credits

  The Linked Data Cloud is maintained by Richard Cyganiak and Anja Jentzsch.

  [Auer07] S. Auer et al., DBpedia: A Nucleus for a Web of Open Data, Proc. ISWC 2007

  [Kobi09] G. Kobilarov et al., Media Meets Semantic Web – How the BBC Uses DBpedia and Linked Data to Make Connections, Proc. ESWC 2009

  [Rai08] Y. Raimond et al., A Web of Musical Information, Proc. ISMIR 2008

  [Hass09] O. Hassanzadeh et al., Linked Movie Data Base, Proc. LDOW 2009


Web of Data in the Context of Multimedia Part 1: Linked Open Data: Vision, Concepts and Technologies

Linking Data




Linking Data   RDF links enable Linked Data browsers and crawlers

to navigate between data sources and to discover additional data.

  Properties used to link data depend on the application domain, e.g. :person1 foaf:knows :person2

  Use owl:sameAs for URI aliases when two URIs refer to the same thing


Linking Data Example: Equivalent URIs for

http://data.linkedmdb.org/resource/film/2014 owl:sameAs 1.http://dbpedia.org/resource/The_Shining_(film) 2.http://data.linkedmdb.org/resource/film/2014 3.http://rdf.freebase.com/ns/guid.9202a8c04000641f800000000046c3da

  Linking can be de done   manually

  automatically


Setting RDF links manually   Usually only done in very small datasets like

personal FOAF profiles (e.g. stating who you know by setting foaf:knows links)

  Look up URI for the resource that you want to link to   uriqr.com

  sindice.com

  (SPARQL) queries to existing datasets

  Use the URI identifying the resource,

  http://dbpedia.org/resource/The_Shining_(film) not the URI for the document about it

  http://dbpedia.org/page/The_Shining_(film)


Auto-generating RDF links   Manual approach not feasible for larger datasets

  Record linkage well-known problem in the DB world

  Specialised pattern-based algorithms for individual problems   Use of unique identifiers (e.g. ISBN for books, ISIN for financial

securites, ISO-3166 country codes, etc.)

  Example:   http://dbpedia.org/resource/Harry_Potter_and_the_Half-Blood_Prince

has a property dbpprop:isbn 747581088

  owl:sameAs link can be easily generated to http://www4.wiwiss.fu-berlin.de/bookmashup/books/0747581088


Tools for data interlinking   Input: 2 (or more) datasets + linkage specification   Output: links between the datasets

Domain-independent tools:   SILK   ODD-Linker   RDF-AI   Knofuss

Domain-specific tools:   LD-Mapper (Music Ontology)   RKB co-reference resolution system (publications)


Overview

RKB CRS LD-Mapper ODD RDF-AI Silk Knofuss

Ontologies multi multi single single single multi

Automation semi automatic semi semi semi semi

User input ad-hoc program none link spec. query

dataset structure alignment method

links spec. alignment method

merged ontology

Input format Java Prolog LinQL XML Silk-LSL (XML) OWL

Matching techniques string

string, similarity propagation string, Wordnet string string

string, adaptive learning

Onto. alignment no no no no no yes, as input

Output owl:sameAs owl:sameAs linkset linkset

alignment format, merged dataset linkset

alignment format, merged dataset

Data access API local copy ODBC local copy SPARQL local copy

Domain publications Music Ontology independent independent independent independent

Overview generated by François Scharffe and Jérôme Euzenat http://melinda.inrialpes.fr


Specification formats

datasets resources links matching

Silk-LSL SPARQL endpoint, graphs name

resources to interlink, resources type

link condition (for each resource)

string matching, matchers combination

Knowfuss local copy (SPARQL query) fusion method string matching (for each resource)

RDF-AI local copy resource descriptions link description fuzzy string, wordnet

LD-Mapper local copy resource query link description string matching

ODD-linker local copy resource description (table.column) link description,

synonym, hyponym, weightedJaccard, token intersect

Overview generated by François Scharffe and Jérôme Euzenat http://melinda.inrialpes.fr


SILK   Silk - A Linking Framework for the Web of Data

  http://www4.wiwiss.fu-berlin.de/bizer/silk/

  Silk Link Specification Language

  User specifies the type of resources to be linked and the comparison technique to be used

  Silk uses many string comparison techniques, numerical and date similarity measures, concept distances in a taxonomy


SILK   Input: 2 datasets behind SPARQL endpoint + LSL

specification

  Output: linkset with owl:sameAs (or other user specified property) links between resources

  Silk LSL example on next slide


<Interlink id="cities">

<LinkType>owl:sameAs</LinkType>

<SourceDataset dataSource="dbpedia" var="a">

<RestrictTo>

?a rdf:type dbpedia:City

</RestrictTo>

</SourceDataset>

<TargetDataset dataSource="geonames" var="b">

<RestrictTo>

?b rdf:type gn:P

</RestrictTo>

</TargetDataset>

<LinkCondition>

<AVG>

<Compare metric="jaroSimilarity">

<Param name="str1" path="?a/rdfs:label" />

<Param name="str2" path="?b/gn:name" />

</Compare>

<Compare metric="numSimilarity">

<Param name="num1" path="?city1/dbpedia:populationTotal" />

<Param name="num2" path="?city2/gn:population" />

<Compare>

</AVG>

</LinkCondition>

<Thresholds accept="0.9" verify="0.7" />

<Output acceptedLinks="accepted_links.n3"

verifyLinks="verify_links.n3"

mode="truncate" />

</Interlink>


Web of Data in the Context of Multimedia Part 1: Linked Open Data: Vision, Concepts, and Technologies:

Consuming Linked Data




Agenda   URI Discovery

  Data Discovery

  Data Set Discovery

  Tools and Libraries to Access and Consume Linked Data   Mashups and Browsers

  Programmatic Access to Linked Data


URI Discovery 1.  Querying specific data sources,

e.g., http://lookup.dbpedia.org

2.  Using dedicated search engines, e.g.,

  Falcons http://iws.seu.edu.cn/services/falcons/

  Sindice http://sindice.com

  SWSE http://www.swse.org

  Watson http://watson.kmi.open.ac.uk


Example Search Engine: Falcons

(1) Entry of keywords

(2) Results of objects

(3) Class hierarchy to refine search

Try yourself: http://iws.seu.edu.cn/services/falcons/


Data Discovery 1.  Manual link traveral (i.e. follow rdfs:seeAlso or

owl:sameAs links)

2.  Use of co-reference services, e.g. http://sameas.org

3.  Use of Uri-based query engines, e.g. http://sindice.org


Sameas.org


Sindice.org


Data Set Discovery 1.  Manually, i.e., by browsing and selecting a data set

from http://esw.w3.org/topic/SparqlEndpoints

2.  (Semi-) automatically, i.e., by exploiting VoiD, the Vocabulary of interlinked Datasets


Describing Datasets   The problem:

  Only human comprehensible descriptions of datasets available

  Automation of tasks impossible such as   Efficient & effective search

  Selection of datasets (for apps, interlinking targets)

  Generation of maps, etc.

  Solution: voiD, the “Vocabulary of Interlinked Datasets” provides a formal description of   What a dataset is about (topic, technical details).

  How and under which conditions to access it.

  How the dataset is interlinked with other datasets.

  Qualitative level: type of interlinking.

  Quantitative level: number of links, resources, etc.

  How to discover the metadata.

cf. K. Alexander, R. Cyganiak, M. Hausenblas, and J. Zhao "Describing Linked Datasets" Proceedings of LDOW 2009, 2009.


VoiD – Core concepts   A dataset is a set of RDF triples that are published, maintained or

aggregated by a single provider.

  A dataset is authoritative with respect to a certain URI namespace if it contains information about resources named by URIs in this namespace, and is published by the URI owner.

  A linkset LS is a set of RDF triples where for all triples ti=⟨si,pi,oi⟩ ∈ LS, the subject is in one dataset, i.e. all si are described in DS1 , and the object is in another dataset, i.e. all oi are described in DS2 .



voiD Vocabulary



voiD Usage Example



Tools and Applications to Consume Linked Data

  Linked Data browsers   To explore things and datasets and to navigate between them.

  Tabulator Browser (MIT, USA), Marbles (FU Berlin, DE), OpenLink RDF Browser (OpenLink, UK), Zitgist Dataviewr (Zitgist, USA), Disco Hyperdata Browser (FU Berlin, DE), Fenfire (DERI, Ireland)

  Linked Data mashups   Sites that mash up (thus combine Linked data)

  Revyu.com (KMI, UK), DBtune Slashfacet (Queen Mary, UK), DBPedia Mobile (FU Berlin, DE), Semantic Web Pipes (DERI, Ireland)

  Search engines   To search for Linked Data.

  Falcons (IWS, China), Sindice (DERI, Ireland), MicroSearch (Yahoo, Spain), Watson (Open University, UK), SWSE (DERI, Ireland), Swoogle (UMBC, USA)

Listing on this slide by T. Heath, M. Hausenblas, C. Bizer, R. Cyganiak, O. Hartig


Example Linked Data Browser: Marbles

  Server-based Linked Data browser.

  Formats RDF for XHTML using Fresnel.

  Unique feature: Indicates the origin of displayed data using colored dots.

  Support for different views:   Full view: all available data is displayed.   Summary view: returns a short textual summary about a resource.

  Photo view: provides a photo for a given resource.

  Retrieves data from multiple sources by (a) issuing parallel queries to multiple Linked Data search engines and (b) by following owl:sameAs and rdfs:seeAlso links.


Example Linked Data Browser: Marbles (2) (1) Entry of query URL

(2) Data display

(3) Sources

Try yourself: http://marbles.sourceforge.net/


Example Linked Data Browser: gFacet

cf. Heim, P., Ziegler, J., and Lohmann, S. "gFacet: A Browser for the Web of Data" In Proceedings of IMC-SSW 2008, 2008. Try yourself: http://gFacet.org


Example Mashup: Revyu.com

Try yourself: http://revyu.com Picture from revyu.com


Example Mashup: DBPedia Mobile

Try yourself: http://wiki.dbpedia.org/DBpediaMobile

Pictures from DBPedia Mobile


Libraries to Programmatically Access the Web of Data

  SPARQL JavaScript Library, http://www.thefigtrees.net/lee/blog/2006/04/sparql_calendar_demo_a_sparql.html

  ARC for PHP, http://arc.semsol.org/

  RAP – RDF API for PHP http://www4.wiwiss.fu-berlin.de/bizer/rdfapi/index.html

  SPARQL Wrapper (Python), http://sparql-wrapper.sourceforge.net/

  PySPARQL (Python), http://code.google.com/p/pysparql/

  DARQ (Distributed ARQ), http://darq.sourceforge.net/

  Semantic Web Client library (SWClLib) for Java, http://www4.wiwiss.fu-berlin.de/bizer/ng4j/semwebclient/

Listing on this slide by O. Hartig, J. Sequeda


What’ll come next   Part 2: Linked Multimedia

Technology

SAMT09 - Web of Data Tutorial - Part 1