SAMT09 - Web of Data Tutorial - Part 1

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

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

Agenda
  Introduction   Multimedia Interlinking

  Producing Linked Data   Multimedia Annotations

  Existing Data Sets   Enriching Personal
Media Collections
  Linking Data

  Consuming Linked Data


Introduction: The Web of Data Vision


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

Genre: Horror/Thriller Release Date: 23 May
1980 (USA)

Title: The Shining Distributors: Warner Bros. Pictures Distribution

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

Starring: Jack
Nicholson, Shelly Produced by: Stanley Kubrick
Duvall, Danny Lloyd, …


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


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


Agenda


Media Collections
  Linking Data


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

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

Text
Text

  SPARQL endpoint must support DESCRIBE queries
  supports multiple datasets (SPARQL endpoints)

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 ;!
Text

§  ex:revenue "C4"^^xl:Expr .!


Agenda


Media Collections
  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) 10/2007
Graz, Austria - 2 Dec 2009

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

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


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
dataset structure links spec.
alignment alignment merged
User input ad-hoc program none link spec. query method method ontology
Silk-LSL
Input format Java Prolog LinQL XML (XML) OWL
Matching string, similarity string, adaptive
techniques string propagation string, Wordnet string string learning

Onto. alignment no no no no no yes, as input
alignment alignment
owl:sameAs format, merged format, merged
Output owl:sameAs linkset linkset dataset linkset 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
SPARQL endpoint, resources to interlink, link condition (for string matching,
Silk-LSL graphs name resources type each resource) matchers combination
string matching (for
Knowfuss local copy (SPARQL query) fusion method each resource)

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

LD-Mapper local copy resource query link description string matching
synonym, hyponym,
resource description weightedJaccard,
ODD-linker local copy (table.column) link description, 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>


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.


Marbles (2) (1) Entry of query URL

(2) Data display

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

(3) Sources

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

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

Example Mashup: DBPedia
Mobile

Pictures from DBPedia Mobile

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

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


SAMT09 - Web of Data Tutorial - Part 1

SAMT09 - Web of Data Tutorial - Part 1

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