1. Introduction to semantic web

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15 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

106 εμφανίσεις

Clément Troprès
-

Damien Coppéré

1

Semantic Web

Based on:

-
The semantic web

-
Ontologies Come of Age

Clément Troprès
-

Damien Coppéré

2

Plan


Introduction to semantic web





Kwnoledge Representation



Ontologies



Agents

Clément Troprès
-

Damien Coppéré

3

1. Introduction to semantic web


Today, most of the web contents is designed
for human to read



The actual web looks insufficient



The semantic web purpose is to structure the
world wide web

Clément Troprès
-

Damien Coppéré

4

1. Introduction to semantic web


Principles:


1.
Each object of the web has a metadata

2.
Each metadata is readable by agents and humans

3.
Each metadata represents accurately an object

4.
Each metadata is available in a common space,
readable by agents and humans. The selection of the
metadata makes the object avalaible as a resource

Clément Troprès
-

Damien Coppéré

5

1. Introduction to semantic web

The semantic web architecture

Clément Troprès
-

Damien Coppéré

6

2. Knowledge representation (1):



Technology which permits computers to access to
structured collections of information



System must have sets of inference rules that
computers can use to conduct automated reasoning




It has to be linked into a single global system




Clément Troprès
-

Damien Coppéré

7

2. Knowledge representation (2) :




Traditional systems usually :



-

Limit the questions that can be asked



-

Become unmanageable



New systems, in contrast, accept paradoxes



-

Unanswerable questions are a price that must

be paid to achieve versatility.



Clément Troprès
-

Damien Coppéré

8

2. Knowledge representation (3) :




Two important technologies exist :



-

EXtensible Markup Language (XML)



-

Resource Description Framework (RDF)



XML :



-

Everyone can create their own tags



-

It allows to add arbitrary structure to the document



Clément Troprès
-

Damien Coppéré

9

2. Knowledge representation (4) :


RDF :



-

Encode in sets of triplets



-

Each triple being rather like the
subject
,
predicate
and
object
of

an

elementary sentence identified by URIs



-

Natural way to describe the vast majority of the data processed

by

machines



-

Example :
New York

has a
postal abbreviation

which is
NY




<rdf:Description rdf:about="
urn:states:New%20York
">
<
"
http://purl.org/dc/terms
/"
:
alternative
>
NY
</rdf:Description>



Universal Resource Identifier




-

Ensure that concepts are tied to a unique definition that

everyone can find on the Web

Clément Troprès
-

Damien Coppéré

10

3. Ontologies
-

Introduction


Current web :


It has grown and continues to grow very quickly


Problems to find information you are really looking for


Designed for human perception



Semantic web:


Make the web understandable by computers agent


Clément Troprès
-

Damien Coppéré

11

3. Ontologies
-

Introduction


How make the web semantic?



-

Complete HTML tag (with XML)



-

Organize the keywords in each document



-

Indexing all the resources of the web (RDF)



-

Ontologies

Clément Troprès
-

Damien Coppéré

12

3. Ontologies
-

Introduction

We are

here

Clément Troprès
-

Damien Coppéré

13

3. Ontologies
-

Introduction


Definition:


-

In 1993, Gruber propose his definition (which is now the
most cited in AI) :



«
An ontology is an
explicit specification
of a


conceptualization
». (Gruber T., 1993b)



-

In 1997, Borst modified slightly the definition in order to
highlight major aspects of this paradigm:



«
An ontology is a
formal specification
of a
shared

conceptualization
». (Borst W. N., 1997)

Clément Troprès
-

Damien Coppéré

14

3. Ontologies
-

Introduction


Definition:


In 1998, these two definitions were only one in the definition
of Studer.



«
An ontology is a
formal
,
explicit specification
of a
shared
conceptualization
». (Studer R. et
al
., 1998)



-

«
Conceptualization
»
refers to an abstraction of a
phenomenon obtained by identifying the concepts appropriate
to this phenomenon



-

«
Shared
» m
eans that ontology captures consensual
knowledge

Clément Troprès
-

Damien Coppéré

15

3. Ontologies
-

Introduction


«
Formal
»
means that ontology is interpretable by a
machine (machinereadable)



«
explicit specification
»
means that the concepts of
ontology and the constraints related to their use are
defined in a declaratory way



Ontology has the following characteristics
:


1)
shared
, 2)
explicit
, 3)
formal


Clément Troprès
-

Damien Coppéré

16

3.Ontologies


Possible representation?


A controlled vocabulary (eg: Catalogs)


A glossary (list of terms)


Thesauri (synonym relationship…, but not an explicit
hierarchy)


Term hierarchies (without true subclass)


Strict subclass hierarchies


Frames (classes include property information)


Value restriction (eg: a price is a number)


Logical deduction

A

B

A is a superclass of B

Clément Troprès
-

Damien Coppéré

17

3. Ontologies


Simple Ontologies


Some of the ways that simple ontologies may be used in
practice:


-
A controlled vocabulary (beginning of interoperability)

-
Site organization and navigation support

-
Expectation setting

-
Umbrella structures from which to extend content

-
Browsing support

-
Search support

-
Sense disambiguation support


Clément Troprès
-

Damien Coppéré

18

3. Ontologies


Structural Ontologies



-
Consistency checking

-
Completion

-
Interoperability support

-
Support validation and verification testing

-
Encode entire test suites

-
Configuration support

-
Support structured, comparative and customized search

-
Exploit generalization/specialization information


Clément Troprès
-

Damien Coppéré

19

3. Ontologies


Implications and Needs


An ontology
-
based application has two major
concerns:



The language



The environment

Clément Troprès
-

Damien Coppéré

20

3. Ontologies


Implications and Needs (1)


The language:


Simple ontologie: It’s not a real problem (language
with subclass and instance relationships)


Structural ontologie: the language must be able to
express the entire domain unambiguously (KRSS,
KIF, OKBC)

Clément Troprès
-

Damien Coppéré

21

3. Ontologies


Implications and Needs (2)


Environment:




Ontology tools are needed to analyze,

modify and maintain an ontology over

time




Many are avalaible commercially

Clément Troprès
-

Damien Coppéré

22

3. Ontologies


Implications and Needs (3)


Environment


Criterias needed :


-

Collaboration and distributed workforce support (share
session)

-

Platform interconnectivity (able to read and write
compatible formats)

-

Scale (In terms of size of ontologies, number of
simultaneous users)

-

Versioning (Able to support many versions of ontology)

Clément Troprès
-

Damien Coppéré

23

3. Ontologies


Implications and Needs (4)


Environment


Major criteria of performance :


-

Security

-

Analysis (focus the user’s attention in areas which need
modification)

-

Lifecyle issues (Support for ontology evolution issues)

-

Ease of use (training materials, tutorials…)

-

Diverse user support

-

Presentation style

-

Extensibility (Adapt along with the needs)

Clément Troprès
-

Damien Coppéré

24

4. Agents


Representing by programs :


-

Collect Web content from diverse sources


-

Process the information


-

Exchange the results with other programs



All agents can work together

Clément Troprès
-

Damien Coppéré

25

4. Agents (2)



Important facets :


-

"Proofs" written in the Semantic Web's unifying
language (Proof Markup Language PML)

-

Digital signatures used to verify that the attached
information has been provided by a specific trusted
source



Example of agent :
You answer your phone and the
stereo sound which was working is turned down.


Clément Troprès
-

Damien Coppéré

26

4. Agents (3)



You want to buy a car …

An intelligent Agent is going to find your new car

-

How ?

It looks for all cars which corespond to your criterias

-

Which criteria ?

Prices,
delivery period, colour…


-

Where ?


On web documents described by semantic standards
(proofs, digital signature…)








Travel Agency…


Clément Troprès
-

Damien Coppéré

27



-

L
ets anyone express new concepts with

minimal effort



-

Unifies a logical language


The Semantic Web