cse 428 semantic web topics introduction

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CSE 428 Semantic Web Topics Introduction Jeff Heflin Lehigh University

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CSE 428 Semantic Web Topics Introduction. Jeff Heflin Lehigh University. The Semantic Web. “Semantic” + “Web” Semantic: "of or relating to meaning in language" (Def. Webster’s) Web: The World Wide Web Official Definition - PowerPoint PPT Presentation

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Page 1: CSE 428 Semantic Web Topics Introduction

CSE 428Semantic Web TopicsIntroduction

Jeff Heflin

Lehigh University

Page 2: CSE 428 Semantic Web Topics Introduction

The Semantic Web

“Semantic” + “Web”– Semantic: "of or relating to meaning in

language" (Def. Webster’s)– 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)

Page 3: CSE 428 Semantic Web Topics Introduction

Why Study Semantic Web?

Open source Semantic Web tools– from IBM, Hewlett-Packard, Nokia, etc.

Commercial software vendors– Oracle 11g RDBMS supports RDF and much of OWL– Adobe’s products use RDF to provide metadata for documents, photos– Semantic Web specific companies: TopQuadrant, Aduna Software, etc.

~65 million Semantic Web documents (as of October 2009)– Yahoo SearchMonkey uses RDF to present richer search results– Google now indexes RDFa (a means for embedding RDF in web pages)

Semantic Web enabled sites– Data.gov: much of U.S. government’s open data is available in RDF– Newsweek: annotates articles with RDFa – BBC Music: exports RDF playlists, RDF for all artists– Harper’s Magazine: connects articles to events on a timeline– DBPedia: a Semantic Web version of Wikipedia

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Semantic Web Standards

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

World Wide Web Consortium (W3C) Recommendations

u:Chair

John Smith

rdf:typeg:name

g:Person

g:name

rdfs:Class rdf:Property

rdf:typerdf:type

rdf:type

rdfs:subclassOf

rdfs:domain

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

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

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Semantic Web Layer Cake

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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

Foaf

DBLP CongressCiteseer

AIGP NSF Awards

extends

extends

extends extends

S3

S7

commits to

commits to

commits to

The answer to a user’s query might require the combination of data from S1, S2, S3, and S4.

Region

S1 S2

Dublin Core

S5

extends

S4

S6

commits to

commits to commits to

extends

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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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Description Logic (DL)

form of knowledge representation– useful for formally defining classes– studied extensively in 1990’s– 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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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

Mar. 1996 - SHOE 0.90 (simple frames in HTML)

Jan. 1998 –SHOE 1.0 (frames + Horn logic)

Feb. 1998 – XML (semi-structured data for Web)

1996 20042000 20021998

Sep. 1998 – Berners-Lee’s Semantic Web Roadmap

Feb. 1999 –RDF (semantic nets in XML)

Mar. 2001 – DAML+OIL (expressive DL in RDF)

May 2001 – Berners-Lee et al. Scientific American article

June. 2002 – 1st Int’l Semantic Web Conference

Feb. 2004 – OWL (W3C Rec.)