SECO: Mediation Services for RDF Data Integration

Andreas Harth (DERI/National University of Ireland, Galway)

http://sw.deri.ie/~aharth/

Thanks to #rdfig for inspiration

What is the Problem?

People use RDF and put RDF data online

This is great, but: how to make use of all the data?

The Web of RDF Data

Annotated photos
FOAF "homepages"
Blogs
iCal
...

Friend-of-a-Friend (FOAF)


	<rdf:RDF
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
      xmlns:foaf="http://xmlns.com/foaf/0.1/">

  <foaf:Person>
    <foaf:name>Andreas Harth</foaf:name>
    <foaf:firstName>Andreas</foaf:firstName>
    <foaf:surname>Harth</foaf:surname>
    <foaf:nick>aharth</foaf:nick>
    <foaf:mbox rdf:resource="mailto:andreas.harth@deri.ie"/>
    <foaf:homepage rdf:resource="http://www.harth.org/andreas/"/>
    <foaf:phone rdf:resource="tel:+353-91-512-651"/>
    <foaf:workplaceHomepage rdf:resource="http://www.deri.ie/"/>
    <rdfs:seeAlso rdf:resource="http://www.isi.edu/~aharth/foaf.rdf"/>
    <foaf:knows>
      <foaf:Person>
	<foaf:name>Jose Luis Ambite</foaf:name>
	<foaf:mbox rdf:resource="mailto:mailto:ambite@isi.edu"/>
	<rdfs:seeAlso rdf:resource="http://www.isi.edu/~ambite/foaf.rdf"/>
      </foaf:Person>
    </foaf:knows>
  </foaf:Person>
</rdf:RDF>

RDF Site Summary (RSS 1.0)

<rdf:RDF
 xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
 xmlns="http://purl.org/rss/1.0/"
 xmlns:dc="http://purl.org/dc/elements/1.1/"
 xmlns:slash="http://purl.org/rss/1.0/modules/slash/"
 xmlns:syn="http://purl.org/rss/1.0/modules/syndication/">

   ...

   <item rdf:about="http://slashdot.org/article.pl?sid=04/05/21/1245258">
      <title>Internet Grocery Shopping Slowly Gaining Ground</title>
      <link>
        http://slashdot.org/article.pl?sid=04/05/21/1245258
      </link>
      <description>
        bakreule writes "Online grocery shopping, once the laughing stock of the
        internet, has quietly started gaining ground. It seemed that the idea had
        been killed ...
      </description>
      <dc:creator>michael</dc:creator>
      <dc:subject>internet</dc:subject>
      <dc:date>2004-05-21T13:29:00+00:00</dc:date>
      <slash:department>three-bags-of-cheetos</slash:department>
      <slash:section>articles</slash:section>
      <slash:comments>99</slash:comments>
      <slash:hitparade>99,95,84,58,28,12,5</slash:hitparade>
   </item>
</rdf:RDF>

The Web of RDF Data

Annotated photos
FOAF "homepages"
Blogs
iCal
...

→ Islands of machine-readable data.

Solution

SECO integrates all kinds of RDF data.

RDF data plus possibly lots of other sources (MySQL databases, IMAP4, search engines...)

Google vs. SECO

Search Engine	Data Integration
documents	data
crawl documents	access databases
mirror the web	distributed architecture
build index/calculate rankings once a week/month	integration on demand
specialized indices for web sites, newsgroups, pictures...	schema mapping
keyword search on index	queries

Big Picture

RDF Crawler: Scutter

Scutter harvests RDF files online and puts them into an RDF repository
FOAF uses rdfs:seeAlso that link files
similar to HTML crawler (robots.txt, breadth-first, etc.)

Scutter

`rdfs:seeAlso`

Wrappers/Legacy Data Sources

Provide RDQL query facilities for:

IMAP4
Google
all kinds of databases

Search engine wrapper

All SECO Components...

... have an RDQL interface and return RDF as result

"A mediator is a software module that exploits encoded knowledge about some sets or subsets of data to create information for a higher layer of applications." (Widerhold 1992).

Parallel Access

intial architecture: distribute queries based on predicates
perform union on graphs for result merging
distribute storage of RDF graph to n data sources

Parallel Access

Object Consolidation

merge based of foaf:mbox
other merging methods possible: heuristics (foaf:name for example)


      substitute bnodes



    
      Object Consolidation
    

    Schema Mapping

    
      
	Mediated term
	Native term
      
      
	title
	dc:title, rss:title, foaf:name, ical:summary, gg:title
      
      
	desc
	dc:description, rss:description, foaf:mbox, ical:description, gg:snippet
      
      
	date
	dc:date, ical:value, gg:date
      
    

    
      map from foaf, rss, nsrss, ical, gg to mediated schema
      mapping currently carried out on predicates
    

    
      Schema Mapping
    

    User Interface
    
      stores usage data for ranking
      a set of pages consists of RDQL queries and corresponding XSLT stylesheet
      from content over structure to presentation
    

    
      
    

    
      User Interface
    

    Implementation
    
      Implemented in Java.
    
    
      Jena2
      HSQLDB Java database (or any JDBC database)
      Ant/JUnit
      Jetty Servlet Container
    

    Summary of Demo
    
      integration of FOAF files, W3Photo, and legacy data source (Google) into a nice user interface
      more data sources can be easily added, if they have RDQL/RDF interface
      SECO applies database ideas — the mediator notion — to data on the Web
    

    Future Work
    
      query language standard: RDQL++?
      query optimization
      need more data
      thumbs up for DAWG and SWBPDWG
      evolve web of linked documents to web of linked RDF repositories (p2p)
    

    Pointers
    
      SECO demo at http://seco.semanticweb.org/ 
    
    
      SECO homepage with source under BSD-style licence at http://sw.deri.ie/2003/seco/.
    
    
      Article in IEEE Intelligent Systems: Semantic Web Challenge.
    
    
      Thanks to Stefan Decker and Jose Luis Ambite for discussion and support.

Mediated term	Native term
title	dc:title, rss:title, foaf:name, ical:summary, gg:title
desc	dc:description, rss:description, foaf:mbox, ical:description, gg:snippet
date	dc:date, ical:value, gg:date