Semantic Web

Taming the Wild Web - An Introduction to the Semantic Web

Dr. Jeff Heflin, Computer Science and Engineering
Lehigh University

• More than 21% of humanity has used the web
• Web can be used for more than you think
• By tracking flu-related queries, Google can determine flue outbreaks faster than reported by the CDC.
• What if we had richer data?

Definition

• The semantic web is not a separate web, but an extension of the current one, in which information is given well-defined meaning, better enabling computers and people to work in cooperation (Berners-Lee et al., 2001).

Ontology

• a key component of the Semantic Web
• ontologies define the semantics of the terms used in semi-structured web pages
  • identify context, provide shared definitions
  • has a formal syntax and unambiguous semantics
  • usually includes a taxonomy but typically much more
• interface algorithms can compute what logically follows

W3C Recommendations

• RDF(S) (1999, revised 2004)
  • directed graphs labeled with URIs
  • XML serialization syntax
• OWL (2004)
  • extends RDF with more semantic primitives
  • based on description logics (DLs)
  • has a model theoretic semantics

<owl:Class rdf:ID="Band">
 <rdfs:subClassOf>
  <owl:Restriction>
   <owl:onProperty rdf:resource="#hasMember" />
   <owl:allValuesFrom red:resource="#Musician" />
  </owl:Restriction>
 </rdfs:subClassOf>
</owl:Class> 

A band is a subset of the groups which only have Musicians as members

URI (Uniform Resource Identifier)

• Includes URLs
• also anything that you can design an identification scheme for
• helps to prevent collision of names
• all the "symbols" in RDF are either URIs or Literals

Namespace

• a mechanism for abbreviating

Description Logic

• Form of knowledge representation
  • Useful for formally defining classes
  • Studied extensively in the 1990s
  • mature reasoning software
    • e.g., FaCT, RACER, Pellet
• benefits
  • optimized computation of subsumption
    • calculate implicit subClassOf relations
  • ontology integration

Level of Adoption?

• Open source Semantic Web tools
• Commercial software vendors (Oracle, Adobe)
• ~65 million Semantic Web documents (as of October 2009)
  • Yahoo SearchMonkey uses REF to present richer search results
  • Google now indexes RDFa
• Semantic Web Enabled Sites
  • BBC Music
  • Harper's Magazine
  • DBPedia
  • LiveJournal uses FOAF

Linking Open Data Project

An Application: Hawkeye

• Requested 1.7 million real Semantic Web documents identified by Swoogle (swoogle.umbc.edu)
• Loaded 760,000 documents, 16.280 ontologies and 166 million triples
• conversion of Citeseer, DBLP, NSF award data and various e-Gov sources
• Developed ontologies to map different schemas
• Developed sources that equate individuals from different sources
• Use OWL as mapping language
• Mapping Ontologies
• Individual Equivalence Statements

Conclusion

• Web is a powerful tool
• Semantic Web is approaching critical mass
• We have demonstrated the feasibility of large-scale integration using OWL
• Integration can emerge via social web processes

Future work

• User-friendly interface
• improved performance
• support more complex reasoning
• support for updates