by Serge Linckels University of Luxembourg 2017/2018

1. Faculty of Science, Technology and Communication (FSTC)
Bachelor en Informatique (professionnel)
Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 1
Semantic Web
Unit 2: Semantic Web – Overview

2. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 2
2. Semantic Web – Overview
2.1. About the "Classical" Web
2.2. Introduction to Semantics
2.3. Vision of the Semantic Web
2.4. Closer Look at HTML
2.5. Lessons Learned
2.6. Semantic Web Architecture
2.7. Applications of the Semantic Web
2.9. References
2.8. Conclusion
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3. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 33
2.1. About the "Classical" Web
2. Semantic Web – Overview

4. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 44
"Web 2.0 is the
business revolution in
the computer industry
caused by the move to
the Internet as
platform, and an
attempt to understand
the rules for success
on that new platform."
(Tim O'Reilly, 2003)
"Social Web"
The Web 2.0 is a service-
oriented environment that gives
the users the freedom and
technological means to actively
contribute to Web content
The term "Web 2.0" describes the changing trends
in the use of World Wide Web technology and web
design that aim to enhance creativity,
communications, secure information sharing,
collaboration and functionality of the web.
Although the term suggests a new version of the
World Wide Web, it does not refer to an update to
any technical specifications, but rather to changes in
the ways software developers and end-users utilize
the Web.
Web 2.0 concepts have led to the development and
evolution of web-culture communities and hosted
services, such as social-networking sites, video
sharing sites, wikis, blogs, and folksonomies.
2.1. About the "Classical" Web
2. Semantic Web – Overview

5. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 55
Folksonomy: different
people have different
perceptions of the same
object. Such perceptions
can be grouped to classify
and identify users.
Everyone can tag objects in the
Web (social tagging). The set of
tags gives a tag cloud.
Popular folksonomies :
2.1. About the "Classical" Web
2. Semantic Web – Overview
Microtargeting

6. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 6
Semantic Web
2.1. About the "Classical" Web
2. Semantic Web – Overview
The Web is also a place where:
- computers do the presentation (easy)
- people do the linking and interpreting (hard)
Why not get computers to do more of the hard work?
Web is a service on the Internet
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7. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 7
Semantic Web
2.2. Introduction to Semantics
2. Semantic Web – Overview
Semantics refers to aspects of meaning, as
expressed in language or other systems of signs
Syntax is the study of the structure of sign
systems, focusing on the form, not the meaning
Pragmatics is the study of the practical use of
signs by agents or communities of interpretation
within particular circumstances and contexts
I movies the go to with my wife
I go to the movies with my wife
The movies went to me
Is the window open?
[The asking person may feel cold]
"Classical Web"
Semantic Web
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8. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 8
“... a goal of the Web was that, if the interaction
between person and hypertext could be so
intuitive that the machine-readable information
space gave an accurate representation of the
state of people's thoughts, interactions, and work
patterns, then machine analysis could become
a very powerful management tool, seeing
patterns in our work and facilitating our working
together through the typical problems which
beset the management of large organizations.”
Semantic Web = a vision of Tim Berners-Lee
(Scientific American, May, 2001)
2.3. Vision of the Semantic Web
2. Semantic Web – Overview
Classical Web is build upon HTML (HyperText Markup Language).
Can HTML be used to build the Semantic Web?
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9. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 9
2.4. Closer Look at HTML
2. Semantic Web – Overview
A markup language provides a way to
combine a text and extra information about it,
like structure and layout.
<h1>Christoph Meinel</h1>
<h2>Viola Brehmer</h2>
<ul>
<li>Long Wang</li>
<li>Feng Cheng</li>
<li>Dirk Cordel</li>
<li>Serge Linckels</li>
</ul>
Harald Sack
Christoph Meinel
Viola Brehmer
Long Wang
Feng Cheng
Dirk Cordel
Serge Linckels
Harald Sack
HTML adds structure and
layout to the content.
But neither a machine, nor a
human can understand the
sense of the content.


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10. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 10
2.4. Closer Look at HTML
2. Semantic Web – Overview
Everyone builds Web pages, without rules and discipline.
Attempt for remediation: W3C compatibility initiative
Poor possibilities for querying the Web (mostly by keywords over the
content)
HTML lacks of standardization (incompatibilities between browsers)
HTML lacks of expressivity
No semantics can be expressed
Limitations and problems of HTML:
others…
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11. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 11
2. Semantic Web – Overview
2.5. Lessons Learned
Uncontrolled growth: lots of extensions
causing incompatibilities
Classical Web Semantic Web
Controlled growth according a roadmap
Based on HTML which is not sufficient to
express semantics
Requires new languages and technologies
to express semantics
No reasoning (logical inference) is possible
over the data
Reasoning over data is possible, e.g.,
better search results
How it began
1997, WWW7 in Brisbane, Australia: Tim Berners-Lee presents his Vision about a "Global
Reasoning Web"
1998, WWW8 in Toronto, Canada: Tim Berners-Lee presents the "Semantic Web Roadmap"
2001, Scientific America publishes an article about the vision of the Semantic Web; the
article becomes the most cited reference to the Semantic Web
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12. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 12
2. Semantic Web – Overview
2.6. Semantic Web Architecture
Semantic Web Roadmap:
Controlled growth bottom
up according to this
architecture.
Architecture was (slightly)
modified in the last years.
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13. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 13
2. Semantic Web – Overview
2.6. Semantic Web Architecture
Web pages have multimedia content
Classical Web Semantic Web
A resource can be anything
Composed of Web pages Composed of resources
Each Web page has a URL Each resource has a URI
Web pages are independent sets of
information
Resources depend on applications; they are
processed in a given context
No semantic description of the content Metadata describe semantics of the content
Resource = {(data,metadata), rules}
Data: can be anything
Metadata: textual annotation (Unicode)
Each resource has a Unified Resource Identifier (URI)
in Unicode
Internationalized Resource Identifier (IRI) is a
generalization / complement of URI
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14. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 14
2. Semantic Web – Overview
2.6. Semantic Web Architecture
XML: shared vocabulary
Gives structure to metadata using a specific set of
elements (tags) in a shared domain
Description of how data are to be used (first step to
describe semantics)
Independent and standardized file exchange format
Christoph Meinel
Viola Brehmer
Long Wang
Feng Cheng
Dirk Cordel
Serge Linckels
Harald Sack
<ChairMeinel>
<Professor>
<FirstName>Christoph</FirstName>
<LastName>Meinel</LastName>
</Professor>
<Secretary>Viola Brehmer</Secretary>
<PhDStudent>Long Wang</PhDStudent>
<PhDStudent>Feng Cheng</PhDStudent>
<PhDStudent>Dirk Cordel</PhDStudent>
<PhDStudent>Serge Linckels</PhDStudent>
<FormerPhDStudent>Harald Sack</FormerPhDStudent>
</ChairMeinel>
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15. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 15
2. Semantic Web – Overview
2.6. Semantic Web Architecture
RDF: abstract syntax with formal semantics
Graphical formalism to describe semantic relations
between resources
Sharing of taxonomies and vocabularies
Different serialization formats, e.g., XML
Different query languages, e.g., SPARQL
Christoph Meinel
Prof. Dr
Scientific Director of HPI
Board Member
http://www.hpi.uni-potsdam.de/meinel.html
Resource
Christoph Meinel
full name
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16. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 16
2. Semantic Web – Overview
2.6. Semantic Web Architecture
OWL: ontologies and reasoning
Powerful formalism to represent classes of objects and
their properties in form of ontologies
Sharing of ontologies
Logical inferences over data
Defining rules over data
Powerful reasoning framework, i.e., Description Logics
Set of resources:
Professor{Christoph Meinel}
PhDstudent{Ji, Long, Dirk, Serge}
Properties:
isProfessorOf(Christoph Meinel,Dirk)
isProfessorOf(Christoph Meinel,Ji)
By logical induction:
DoctorFather Professor isProfessorOf.PhDstudent
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17. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 17
2. Semantic Web – Overview
2.6. Semantic Web Architecture
Logic, Proof, Trust
Are the semantic data reliable and trustful?
Have the data been manipulated?
Public key encryption
Digital signatures
Semantic document = resource + set of assertions
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18. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 18
2. Semantic Web – Overview
2.7. Applications of the Semantic Web
Web based applications
Help the user find what (s)he is looking for by a better
understanding of the sense of the query. Example:
"Hotel in Wien with a large bed and a TV set"
Not Web base applications
Personalization of search engines. Example:
The user lives in Wien and prefers a large TV set
Make explicit some implicit knowledge. Example:
Where can I get gasoline? Answer can be the result of a
logicial inference.
Agents (robots) can better index resources on the Web.
Different domains need (and use already) systems that
implement Semantic Web technologies. Examples:
- medicine, pharma industry
- e-Learning
- travel agencies
- digital libraries
- …
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19. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 19
2. Semantic Web – Overview
2.8. Conclusion
The Semantic Web is…
A vision of a new Web that shall replace the "classical Web"
Several technologies were (or are about to be) created to build the Semantic Web
The Semantic Web does not exists yet, but different kind of applications do already
implement related technologies
The Semantic Web is not…
Some kind of artificial intelligence that makes stupid search engines yield better results
The Semantic Web is (still) a hot topic in ongoing research
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20. Semantic Web ::: Serge Linckels ::: www.linckels.lu ::: serge@linckels.lu ::: 20
2. Semantic Web – Overview
2.9. References
Creating the Semantic Web with RDF: Professional Developer's Guide
Johan Hjelm
Foundations of Semantic Web Technologies
Pascal Hitzler, Markus Krötzsch, Sebastian Rudolph
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E-Librarian Service
User-Friendly Semantic Search in Digital Libraries
Serge Linckels, Christoph Meinel