Semantic Web
Hieu Le, Nhung Nguyen, Mayssam
UIUC - CS511 – Fall 2005
(lots of slides browed from: Deborah McGuinness, James Hendler,
Stefan Decker, Mike Lowndes, Mehmet S. Aktas, Steve Cayzer)
Roadmap
Motivation
Broad picture
Zoom in to current state
Zoom in closer to the future
The Holly Grail: A Killer App.
Discussion
Conclusion
Today: Rich Information Source for Human
Manipulation/Interpretation
Human
Human
Human
Human
Tomorrow: Rich Information Source for Agent
Manipulation/Interpretation
Human
Agent
Agent
Doctor’s appointment
“The Semantic Web”, Scientific American, May 2001
Insurance Co.
Rating
Mom Provider sites
Physician’s Agent
required in-plan?
treatment close-by?
Specialist?
Schedule appointment
Driving schedule
Lucy’s Agent Pete’ Agent
Roadmap
Motivation
Broad picture
Zoom in to current state
Zoom in closer to the future
The Holly Grail: A Killer App.
Discussion
Conclusion
The Evolving Web
Web of
Knowledge
Proof, Logic and
Ontology Languages
DATA/PROGRAMS
Shared terms/terminology
Machine-Machine communication
2010
Resource Description Framework
eXtensible Markup LanguageSelf-Describing Documents
2000
DOCUMENTS
HyperText Markup Language
HyperText Transfer ProtocolFoundation of the Current Web
1990
Berners-Lee, Hendler; Nature, 2001
Web Semantics
Semantic Web LayerCake (Berners-Lee, 99;Swartz-Hendler, 2001)
Can’t we just use XML?
This is what a web-page in natural language
looks like for a machine
XML helps
XML allows “meaningful tags” to be added to
parts of the text
XML machine accessible meaning
But to your machine,
the tags look like this….
name
CV
Schemas take a step in the right
direction
Schemas help….
…by relating
private common terms
between documents
But other people use other schemas
Someone else has one like this….
name>
>
The “semantics” isn’t there
private …which don’t fit in
KR provides “external”
referents to merge on
nme
CV
work CV
vate
educ CV
ed
uc
name >
>
And structure.
Current Activities
We
are
here
Semantic Web LayerCake (Berners-Lee, 99;Swartz-Hendler, 2001)
Roadmap
Motivation
Broad picture
Zoom in to current state
Zoom in closer to the future
The Holly Grail: A Killer App.
Discussion
Conclusion
W3C Web Ontology Working Group
• Web Ontology Working Group in the W3C Semantic Web Activity
aimed at “extending the semantic reach of current XML and RDF
meta-data efforts. “
• History
– DAML+OIL is submitted as a joint committee effort published as a
W3C note .
– W3C WG Announcement in November 2001 -
http://lists.w3.org/Archives/Public/www-rdf-
logic/2001Nov/0000.html
– Weekly teleconferences started in November 2001
– First Face to Face Meeting - New Jersey (Lucent), Jan „02; 2nd -
Amsterdam April (W3C); 3rd - CA (Fujitsu/Stanford host) July; 4th
in Bristol UK (HP Host) Oct.
– Four Working Drafts to date
• Requirements/Use cases - March 2002
• 3 Technical Documents - July 2002 (Language renamed OWL)
Membership
• Current Working Group includes over 50 members from over 30 organizations.
– Chairs
• J. Hendler, MIND Lab UMCP
• G. Schreiber, Univ. of Amsterdam
– Industry including:
• Large companies - Daimler Chrysler, IBM, HP, Intel, EDS, Fujitsu, Lucent,
Motorola, Nokia, Philips Electronics, Sun, Unisys
• Newer/smaller companies - IVIS Group, Network Inference, Stilo
Technology, Unicorn Solutions
– Government and Not-For-Profits:
• US Defense Information Systems Agency, Interoperability Technology
Association for Information Processing, Japan (INTAP) , Electricite De
France, Mitre, NIST
– Universities and Research Centers:
• University of Bristol, University of Maryland, University of Southamptom,
Stanford University
• DFKI (German Research Center for Artificial Intelligence),
Forschungszentrum Informatik, Ontoweb
– Invited Experts
• Well-known academics from non-W3C members (Hayes, Heflin, Stein,
Borden)
The Semantic Stack and Ontology Languages
B
OWL Full
DAML, OWL DL
OIL,
DAML+OIL OWL Lite
A RDF Schema
RDF
XML, XML Schema
The Semantic Language Layer for the Web From “The Semantic Web” technical report by Pierce
A = Ontology languages based on XML syntax
B = Ontology languages built on top of RDF and RDF Schema
Resource Description Framework (RDF)
-I
• Resource Description Framework (RDF) is a
framework for
describing and interchanging metadata (data describing the
web
resources).
• RDF provides machine understandable semantics for
metadata.
This leads,
– better precision in resource discovery than full text
search,
– assisting applications as schemas evolve,
– interoperability of metadata.
Resource Description Framework (RDF)-
II
• RDF has following important concepts
– Resource : The resources being described by RDF are
anything that can be named via a URI.
– Property : A property is also a resource that has a name, for
instance Author or Title.
– Statement : A statement consists of the combination of a
Resource, a Property, and an associated value.
Example: Alice is the creator of the resource http://www.cs.indiana.edu/~Alice.
The Dublin Core Definition Standard
• RDF is dependent on metadata conventions for definitions.
• The Dublin Core is an example definition standard which
defines a simple metadata elements for describing Web
authoring.
• It is named after 1995 Dublin (Ohio) Metadata Workshop.
• Following list is the partial tag element list for Dublin Core
standard.
– Creator: the primary author of the content
– Date: date of creation or other important life cycle events
– Title: the name of the resource
– Subject: the resource topic
– Description: an account of the content
– Type: the genre of the content
– Language: the human language of the content.
Example
Alice is the creator of the resource http://www.cs.indiana.edu/~Alice.
Property
Resource
Property
Value
creator
=
http://purl.org/dc/elements/1.1/creator
http://www.cs.indiana.edu/~Alice Alice
• Property “creator” refers to a specific definition. (in this example by Dublin Core
Definition Standard). So, there is a structured URI for this property. This URI makes this
property unique and globally known.
• By providing structured URI, we also specified the property value Alice as following.
“http://www.cs.indiana.edu/People/auto/b/Alice”
Inspired from “The Semantic Web” technical report by Pierce
AIST Meeting JPL, CA 2003
Example Why bother to use
RDF instead of XML?
Alice is the creator of the resource http://www.cs.indiana.edu/~Alice.
Alice
• Information in the graph can be modeled in diff. XML organizations. Human readers would
infer the same structure, however, general purpose applications would not.
•Given RDF model enables any general purpose application to infer the same structure.
Inspired from “The Semantic Web” technical report by Pierce
AIST Meeting JPL, CA 2003
RDF Schema (RDFS ) It resembles
objected-oriented
programming
• RDF Schema is an extension of Resource Description Framework.
• RDF Schema provides a higher level of abstraction than RDF.
– specific classes of resources ,
– specific properties,
– and the relationships between these properties and other resources can be
described.
• RDFS allows specific resources to be described as instances of more
general classes.
• RDFS provides mechanisms where custom RDF vocabulary can be
developed.
• Also, RDFS provides important semantic capabilities that are used by
enhanced semantic languages like DAML, OIL and OWL.
AIST Meeting JPL, CA 2003
Limitations of RDF/RDFS
• No standard for expressing primitive data types such as integer, etc.
All data types in RDF/RDFS are treated as strings.
• No standard for expressing relations of properties (unique, transitive,
inverse etc.)
• No standard for expressing whether enumerations are closed.
• No standard to express equivalence, disjointedness etc. among
properties
AIST Meeting JPL, CA 2003
DAML, OIL and DAML+OIL - I
• RDF\RDFS define a framework, however they have limitations. There is a
need for new semantic web languages with following requirements
• They should be compatible with (XML, RDF/RDFS)
• They should have enough expressive power to fill in the gaps in
RDFS
• They should provide automated reasoning support
• Ontology Inference Layer (OIL) and DARPA Agent Markup Language
(DAML) are two important efforts developed to fulfill these requirements.
• Their combined efforts formed DAML+OIL declarative semantic language.
AIST Meeting JPL, CA 2003
DAML, OIL and DAML + OIL - II
• DAML+OIL is built on top of RDFS.
• It uses RDFS syntax.
• It has richer ways to express primitive data types.
• DAML+OIL allows other relationships (inverse and transitivity) to be
directly expressed.
• DAML+OIL provides well defined semantics, This provides followings:
• Meaning of DAML+OIL statements can be formally specified.
• Machine understanding and automated reasoning can be supported.
• More expressive power can be provided.
AIST Meeting JPL, CA 2003
Example
How is DAML+OIL is
different than RDF/RDFS?
Example: T. Rex is not herbivore and not a currently living species.
• This statement can be expressed in DAML+OIL, but not in RDF/RDFS
since RDF/RDFS cannot express disjointedness.
• DAML+OIL provides automated reasoning by providing such expressive
power.
– For instance, a software agent can find out the “list of all the carnivores that
won’t be any threat today” by processing the DAML+OIL data representation
of the example above.
– RDF/RDFS does not express “is not” relationships and exclusions.
From “The Semantic Web” technical report by Pierce
AIST Meeting JPL, CA 2003
Web Ontology Language (OWL)
• Web Ontology Language (OWL) is another effort developed by the OWL
working group of the W3Consorsium.
• OWL is an extension of DAML+OIL.
• OWL is divided following sub languages.
• OWL Lite
• OWL (Description Logics) DL
• OWL Full – limited cardinality
• OWL Lite provides many of the facilities of DAML+OIL provides. In
addition to RDF/RDFS tags, it also allows us to express equivalence,
identity, difference, inverse, and transivity.
• OWL Lite is a subset of OWL DL, which in turn is a subset of OWL Full.
AIST Meeting JPL, CA 2003
A Note: Having an ontology is
not enough
• The philosophy of WWW and SW is
similar: decentralized
• Ontologies and data formats are different
from sources to sources, time to time.
Ontology matching
Data Integration
A Note: Having an ontology is
not enough
• The philosophy of WWW and SW is
similar: decentralized
• Ontologies and data formats are different
from sources to sources, time to time.
Ontology matching
Data Integration
But will it fly?
• DAML+OIL is already the most used ontology language ever!!
– http://www.daml.org (3.5M statements on 25,000 web pages)
• Gaining acceptance by web players
– Semantic Web Track being offered at WWW 2002
– 3x more people attended WWW2002 Developer Day on SW than
attended KR
• Significant (international) Govt Support
– US DARPA/NSF; EU IST Framework 5,6
– Japan, Germany, Australia considering significant investments
– US National Cancer Institute to publish cancer vocabulary in DAML+OIL
• Much New Startup activity (even in this economic climate)
• Many tools being developed
– Many of them aimed at developers, not just AI literate types
Roadmap
Motivation
Broad picture
Zoom in to current state
Zoom closer to the future
The Holly Grail: A Killer App.
Discussion
Conclusion
Moving to the future of the
web
Semantic Web LayerCake (Berners-Lee, 99;Swartz-Hendler, 2001)
Web Agents need Service
Descriptions
Semantic Web Service
Description
-
-
-
-
-
-
-
Services need Web Logics
Web of Trust
• Claims can be verified if there is supporting
evidence from another (trusted) source
– We only believe that someone is a professor
at a university if the university also claims that
person is a professor, and the university is on
a list I trust.
believe(c1) :- claims(x, c1) ^ predicate(c1, professorAt) ^
arg1(c1, x) ^ arg2(c1, y) ^ claims(c2, y) ^
predicate(c2, professorAt) ^ arg1(c2, x) ^
arg2(c2, y) ^ AccreditedUniversity(y)
AcknowledgedUniversity(u) :- link-from(“http://www.cs.umd.edu/university-list”,u)
Notice this one
Roadmap
Motivation
Broad picture
Zoom in to current state
Zoom closer to the future
The Holly Grail: A Killer App.
Discussion
Conclusion
FOAF:a semweb case study
The Friend of a Friend
(FOAF) project is about
creating a Web of
machine-readable
homepages describing
people, the links between
them and the things they
create and do.
Distributed RDF/XML
records describing
people, who they know,
projects they work on…
FOAF - motivations
• Augment e-mail filtering by prioritizing
mails from trusted colleagues
• Locate people with interests similar to
yours
• „Find an expert‟ in knowledge
communities
• Social network analysis
• Photo co-depiction
A simple foaf model
foaf:Person
rdf:type
foaf:name
Michael Souris
foaf:mbox
mailto:mm@example.com
.. which can be serialized in
XML
Michael Souris
So what?
We need more!
• The history of WWW is a lesson
• We see the potential, but:
– How to convince people to mark up their
pages?
– How to convince organization to export their
data in SW formats?
Answer: We need a Killer Application
We need more!
• The history of WWW is a lesson
• We see the potential, but:
– How to convince people to mark up their
pages?
– How to convince organization to export their
data in SW formats?
Answer: We need a Killer Application
Semantic Web Challenge:
Minimum Requirements
• First, the information sources used
– should be geographically distributed,
– should have diverse ownerships (i.e. there is no
control of evolution),
– should be heterogeneous (syntactically, structurally,
and semantically), and
– should contain real world data, i.e. are more than toy
examples.
• Second, it is required that all applications
assume an open world, i.e. assume that the
information is never complete.
• Finally, the applications should use some formal
description of the meaning of the data.
Semantic Web Challenge:
More Requirements
• The application uses data sources for other purposes or
in another way than originally intended
• Using the contents of multi-media documents
• Accessibility in multiple languages
• Accessibility via devices other than the PC
• Other applications than pure information retrieval
• Combination of static and dynamic knowledge (e.g.
combination of static ontologies and dynamic work-flows)
• The results should be as accurate as possible (e.g. use
a ranking of results according to validity)
• The application should be scalable (in terms of the
amount of data used and in terms of distributed
components working together)
For short, a Killer Application
must provide:
1. A service that is not possible or practical
under more traditional technologies,
2. Some clear benefit to developers, data
providers, and end users with minimum
extra costs
3. an application that becomes
indispensable to a user-base much wider
than the SW researchers community.
Roadmap
Motivation
Broad picture
Zoom in to current state
Zoom closer to the future
The Holly Grail: A Killer App.
Discussion
Conclusion
How do you think?
• Semantic web: Make the web
become a huge distributed
database
Roadmap
Motivation
Broad picture
Zoom in to current state
Zoom closer to the future
The Holly Grail: A Killer App.
Discussion
Conclusion
Conclusion
• It is no longer a question of whether the semantic web will come
into being, it is already here!
• We‟re already well past the starting gate
– Web ontologies, term languages, “shims” to DB and services,
research in proofs/rules/trust
– Standardization providing a common denominator for KR
researchers as well as web developers
– Small companies starting to form, Big companies starting to
move
• Challenges ahead:
– Ontology mapping
– Data Integration
– Finally, a Killer Application
Thanks
On the Web -- links are
critical!
Web page Any Web Resource
HTML
On the Semantic WEB -- links are critical!
URI
URI URI
RDF RDF is like the web! And…
RDF graphs resemble
semantic nets
DOC1
Mind: Jobs: Professor
DOC1 Mind:title
Jobs: Hendler
Jobs:placeOfWork Web Page
http://www…
Semantics on the WEB
• RDF, like the WWW itself, is not “separable”
– Thinking about the ontologies, without considering
• The links to other terms
• The instances that link to them
• The crawling and collecting of ontological terminologues
Is like thinking about the Web without the links!!
Other
Professors
Other
titles Jobs: Professor
Mind: Other
Other Pages
DOC1 Mind:title
URIs
Jobs: Hendler
Jobs:placeOfWork Web Page
Other http://www…
descriptions
Radically new view of Semantics
= some partial mapping
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Distributed,partially mapped, inconsistent -- but SCALEABLE!
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