Semantic Web

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22 Οκτ 2013 (πριν από 3 χρόνια και 8 μήνες)

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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


Mom

Physician’s Agent

Lucy’s Agent

required

treatment

Schedule appointment

Insurance Co.

Provider sites

Rating

in
-
plan?

close
-
by?

Specialist?


Pete’ Agent

Driving schedule

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

HyperText Markup Language

HyperText Transfer Protocol

Resource Description Framework

eXtensible Markup Language

Self
-
Describing Documents

Foundation of the Current Web

Proof, Logic and

Ontology Languages

Shared terms/terminology

Machine
-
Machine communication

1990

2000

2010

Berners
-
Lee, Hendler;
Nature
, 2001

DOCUMENTS

DATA/PROGRAMS

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

CV

name

education

work

private

< >

< >

< >

< >

< >

XML allows “meaningful tags” to be added to

parts of the text

XML


machine accessible meaning

CV

name

education

work

private

< >

< >

< >

< >

< >

<
CV

>

<

name

>

<
education
>

<
work
>

<
private
>

䉵琠瑯ty潵爠浡捨楮攬m

the tags look like this….

Schemas take a step in the right
direction

Schemas help….

<
CV

>

…by relating

common terms

between documents

private

But other people use other schemas

CV

name

education

work

private

< >

< >

< >

< >

< >

<
CV

>

name
>

<
educ
>

<>

<

>

Someone else has one like this….

The “semantics” isn’t there

<
CV

>

…which don’t fit in

private

KR provides “external”
referents to merge on

SW languages add mappings

And structure.

nme

work

vate

educ

CV

CV


CV

ed
uc

CV

name

education

work

private

< >

< >

< >

< >

< >

<

CV


>

<

name

>

<

educ

>

<>

<



>

Current Activities

Semantic Web LayerCake
(Berners
-
Lee, 99;Swartz
-
Hendler, 2001)

We

are

here

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

From “The Semantic Web” technical report by Pierce

The Semantic Language Layer for the Web

A

B

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


AIST Meeting JPL, CA 2003



http://www.cs.indiana.edu/~Alice


creator


=

http://purl.org/dc/elements/1.1/creator

Alice

is the
creator

of the resource
http://www.cs.indiana.edu/~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”

Alice

Resource

Property

Property
Value

Inspired from “The Semantic Web” technical report by Pierce

Example


AIST Meeting JPL, CA 2003



Alice

is the
creator

of the resource
http://www.cs.indiana.edu/~Alice
.








Inspired from “The Semantic Web” technical report by Pierce

<rdf:RDF xmlns:rdf=”
http://www.w3c.org/1999/02/22
-
rdf
-
syntax
-
ns##




xmlns:dc=”
http://purl.org/dc/elements/1.1




xmlns:cgl=”
http://cgl.indiana.edu/people
”>

<rdf:Description about=”
http://www.cs.indiana.edu/~Alice
”>


<dc:creator>



<cgl:staff>
Alice

</cgl:staff>


</dc:creator>

</rdf:RDF>



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.



Why bother to use
RDF instead of XML?


RDF Schema (
RDFS

)



AIST Meeting JPL, CA 2003



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.

It resembles
objected
-
oriented
programming

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


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.

AIST Meeting JPL, CA 2003

How is DAML+OIL is
different than RDF/RDFS?

From “The Semantic Web” technical report by Pierce

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





䑡瑡 䥮瑥杲慴g潮

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





䑡瑡 䥮瑥杲慴g潮

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

Michael Souris

foaf:Person

mailto:mm@example.com

foaf:name

rdf:type

foaf:mbox

.. which can be serialized in
XML

<rdf:RDF

xmlns:rdf="http://www.w3.org/1999/02/22
-
rdf
-
syntax
-
ns#"

xmlns:foaf="http://xmlns.com/foaf/0.1/">



<foaf:Person>


<foaf:name>Michael Souris</foaf:name>


<foaf:mbox rdf:resource="mailto:mm@example.com" />


</foaf:Person>


</rdf:RDF>

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!

<a href=

URI>

HTML

Web page

Any Web Resource

<a href=“http://…”>

RDF

URI

URI

URI

RDF is like the web! And…

On the Semantic WEB
--

links are critical!

<mind:Person rdf:id=“Hendler”>


<mind:title jobs:Professor>


<jobs:placeOfWork
http://www.cs.umd.edu>

</mind:Person>

DOC1

Hendler

DOC1

Mind:title

Jobs:placeOfWork

Web Page

http://www…

Professor

Jobs:

Mind:

Jobs:

RDF graphs resemble
semantic nets

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!!

Hendler

DOC1

Mind:title

Jobs:placeOfWork

Web Page

http://www…

Professor

Jobs:

Mind:

Jobs:

Other

Professors

Other

Pages

Other

title
s

Other

description
s

Other

URI
s

Radically new view of Semantics

Distributed,partially mapped, inconsistent
--

but SCALEABLE!

uses

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= some partial mapping