CSE 428 Semantic Web Topics Introduction

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CSE 428Semantic Web TopicsIntroduction

• Jeff Heflin
• Lehigh University

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The Semantic Web

• Semantic Web
• Semantic "of or relating to meaning in language"
  (Def. Websters)
• Web The World Wide Web
• Official 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., Scientific
  American, May 2001)

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Why Study Semantic Web?

• 2.4 million RDF/OWL documents on the Web (as of
  March 2008)
• LiveJournal automatically creates data using the
  popular Friend-of-a-Friend (FOAF) schema for
  every user
• Yahoo is starting to support Semantic Web
  standards (March 2008)
• Open source Semantic Web tools
• from IBM, Hewlett-Packard, Nokia, etc.
• Commercial software vendors
• Oracle 10g DBMS supports RDF, Oracle 11g has some
  support for OWL
• Adobes products use RDF to provide metadata for
  documents, photos
• Semantic Web specific companies TopQuadrant,
  Aduna Software, etc.
• Companies that have invested in Semantic Web
  solutions
• Boeing integrate work of partners involved in
  airplane design
• Chevron manage the life cycle of power plants
  and oil refineries
• British Telecom online service to help vendors
  work together
• Harpers Magazine web site that connects
  articles to events on a timeline
• Many more

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Semantic Web Standards
World Wide Web Consortium (W3C) Recommendations

• RDF(S) (1999, revised 2004)
• essentially semantic networks with URIs
• XML serialization syntax

• OWL (2004)
• extends RDF with more semantic primitives
• based on description logics (DLs)
• has a model theoretic semantics

rdfsClass
rdfProperty

• 
  rdfresourcehasMember /
  
  Class
• A Band is a subset of the groups which only have
  Musicians as members

rdftype
rdftype
gPerson
rdftype
rdfsdomain
rdfssubclassOf
uChair
gname
rdftype
gname
John Smith
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Description Logic (DL)

• form of knowledge representation
• useful for formally defining classes
• studied extensively in 1990s
• mature reasoning software
• e.g., FaCT, RACER, Pellet
• benefits
• optimized computation of subsumption
• calculate implicit subClassOf relations
• ontology integration
• if two ontologies are related via class
  expressions then subsumption can be used to
  compute an integrated ontology

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Semantic Web Layer Cake
From W3C (March 2007)
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The End
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Motivation

• How to answer these queries?
• find all bills dealing with energy that have
  been sponsored by Congressmen from states with
  populations less than 1 million
• retrieve a list of all papers authored by
  NSF-funded individuals who are located in states
  in the Midwest
• find a potential collaborator by identifying a
  friend-of-a-friend who has written an article on
  a related topic

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The Semantic Web

• 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., Scientific
  American, May 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
• inference algorithms can compute what logically
  follows

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A Web of Ontologies
S1
S2
commits to
extends
Foaf
Dublin Core
Region
extends
extends
extends
Congress
extends
extends
DBLP
Citeseer
commits to
commits to
AIGP
NSF Awards
commits to
S3
S4
S7
commits to
commits to
The answer to a users query might require the
combination of data from S1, S2, S3, and S4.
S5
S6
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URIs and Namespaces

• URI
• Uniform Resource Identifier
• includes URLs
• but 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 URIs
• by assigning a prefix for a URI fragment

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OWL Class Constructors
example taken from Ian Horrocks
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OWL Axioms
example taken from Ian Horrocks
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Common Criticisms

• Who will create all of the RDF/OWL data?
• How do you integrate heterogeneous ontologies?
• How can you handle spam / deceit /
  misinformation?
• How can a system based on formal logic achieve
  Web scale?

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Semantic Web Challenges

• The Web is distributed
• many sources, varying authority
• inconsistency
• The Web is dynamic
• representational needs may change
• The Web is enormous
• systems must scale well
• The Web is an open-world

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Semantic Web Timeline
May 2001 Berners-Lee et al. Scientific
American article
Mar. 1996 - SHOE 0.90 (simple frames in HTML)
Feb. 1998 XML (semi-structured data for Web)
Feb. 1999 RDF (semantic nets in XML)
Feb. 2004 OWL (W3C Rec.)
1996
2004
2000
2002
1998
Jan. 1998 SHOE 1.0 (frames Horn logic)
Sep. 1998 Berners-Lees Semantic Web Roadmap
Mar. 2001 DAMLOIL (expressive DL in RDF)
June. 2002 1st Intl Semantic Web Conference