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241-320 Design Architecture and Engineeringfor Intelligent System

Suntorn Witosurapot

Contact Address: Phone : 074 287369 or

Email: [email protected]

January 2011


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Lecture 18:

Introduction to Semantic Web


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241-320 Design Architecture &Engineering for Intelligent System Introduction to Semantic Web 3

Preview:

In the last chapter, we have learned varioustechniques of Machine Learning , which make thecomputer (or agent) becomes intelligence.

We remain study the same issue in this lecture,, butshift the domain to the Web , which becomes anessential to our daily life.

We will learn how the web content can turn to be a

knowledge base so that it can be searched or queriedin the intellgent manner.


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Outline

Semantic Web BasicsSemantic Web Applications

Semantic Web Services Basics


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Semantic Web

The Semantic Web is an extension of thecurrent web in which information is given well-defined meaning , better enabling computers and

people to work in co-operation .[Berners-Lee et al., 2001]


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Semantic Web Vision


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Todays Web: the Syntactic Web


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The Syntactic Web is

A hypermedia, a digital library A library of documents called (web pages)

interconnected by a hypermedia of links

A database, an application platform A common portal to applications accessiblethrough web pages, and presenting their resultsas web pages

A platform for multimedia BBC Radio 4 anywhere in the world!A naming scheme Unique identity for those documents


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i.e. the Syntactic Web is

A place where computers do the presentation (easy) and

people do the linking and interpreting (hard).

Why not get computers to do more of the hard work?


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Hard Work using the Syntactic Web

Complex queries involving background knowledge Find information about animals that use sonar but

are not either bats, dolphins or whales

Locating information in data repositories Travel enquiries Prices of goods and services Results of human genome experiments

Delegating complex tasks to web agents Book me a holiday next weekend somewhere warm,

not too far away, and where they speak French orEnglish


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What is the Problem?

Consider a typical web page:Markup consists of: rendering

information (e.g.,font size andcolour)

Hyper-links torelated content

Semantic content is

accessible tohumans but not(easily) tocomputers


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What information can we see

WWW2002The eleventh international world wide web conferenceSheraton waikiki hotel, Honolulu, hawaii, USA7-11 may 2002, 1 location 5 days learn interactRegistered participants coming fromaustralia, canada, chile denmark, france, germany, ghana, hong kong,,

norway, singapore, switzerland, the united kingdom, the unitedstates, vietnam, zaire

Register nowOn the 7 th May Honolulu will provide the backdrop of the eleventh

international world wide web conference. This prestigious event..

Speakers confirmedTim berners-leeTim is the well known inventor of the Web, Ian FosterIan is the pioneer of the Grid, the next generation internet


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What information can a machine see


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XML User definable and domain specific markup

Knowledge Management

Manager: John Davies Project: SEKT

HTML:

Knowledge Management John Davies SEKT

XML:


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XML: Document = labelled tree

course

teachertitle students

name http

... ...

......

...

=

DTD: simple grammars to describe legal trees

node = label + contents


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241-320 Design Architecture &Engineering for Intelligent System Introduction to Semantic Web

17

Solution: XML markup with meaningful tags?


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But What About

CV

name

education

work

private

< >

< >


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Only feasible for closed collaboration agents in a small & stable community pages on a small & stable intranet

.. not for sharable Web-resources

XML: limitations for semantic markup

XML makes no commitment on: Domain specific ontological vocabulary

Which words shall we use to describe a given set of concepts? Ontological modelling primitives

How can we combine these concepts, e.g. car is a-kind-of(subclass-of) vehicle

requires pre-arranged agreement on vocab & primitives


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Limitations of the Web today

Machine-to-human, not machine-to-machine


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Limitations of the Web today (cont.)

You can easily search for documents (e.g. via GoogleSearch Engine), but can not extract information


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Limitations of the Web today (cont.)

You can easily search for documents (e.g. via GoogleSearch Engine), but can not extract information


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What should the web be served for?Combining information


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What should the web be served for?Combining information (cont.)


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How can we make the web to do that?

Instead of publishing natural language, publishmachine-processable data !

Publish information in terms understandable for amachine

Ask questions in terms understandable for a machine

And: make sure all machines understand your terms!


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XML is a first step

Semantic markup HTML layout XML meaning

Metadata within documents, not across documents Prescriptive ( ) , not descriptive (

)

No commitment on vocabulary and modellingprimitives

RDF is the next step


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Detour: Flat File Records

Consider the following records in flat file:

011500 18.66 0 0 62 46.271020111 25.220010011500 26.93 0 1 63 68.951521001 32.651010020100 33.95 1 0 65 92.532041101 18.930110020100 17.38 0 0 67 50.351111100 42.160001

What do they mean?


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Detour: Metadata

NAME LENGTH FORMAT LABELinstudy 6 MMDDYY Date of randomization

into studybmi 8 Num Body Mass Index.obesity 3 0=No 1=Yes Obesity (30.0


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Detour: Schema

A flat file is a collection of records.

A record consists of fields.

Each record in a flat file has the same number andkinds of fields as any other record in the same file.

The schema of a flat file describes the structure(i.e., the kinds of fields) of each record.


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Detour: Self-Describing Data

Schema


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RDF is beyond XML

RDF is a language for representing information aboutresources in the web.

While RDF is expressed in XML, it has differentsemantics.

Resource Description Framework

XML RDF

Element Type Class

Element Instance Resource

Data attribute DatatypeProperty

Reference attribute ObjectProperty

Containment Property

XML vs. RDFTerminology


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RDF for semantic annotation

RDF provides metadata about Web resourcesObject -> Attribute-> Value triplesIt has an XML syntaxChained triples form a graph

http://www.aifb.uni-karlsruhe.de/WBS/ysu

site-owner

York 608659

2

telW3C

explains

http://www.w3.org/RDF

site-owner

< rdf:Description rdf:about =#York>< tel >6086592


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What does RDF Schema add?

Defines vocabulary for RDF Organizes this vocabulary in a

typed hierarchy Class, subClassOf, type Property, subPropertyOf domain, range

Rudi York

Person

PhDStud Professor

subClassOf subClassOf

type

hasSuperVisordomain range

typehasSuperVisor

RDFS

RDF


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Conclusions about RDF(S)

Next step up from plain XML: (small) ontological commitment to modeling

primitives

possible to define vocabulary

However: no precisely described meaning

no inference model


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The semantic pyramid again


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The Ontology layer

ontology = shared conceptualization=> conceptual model

(more expressive than RDF + RDFS)

=> expressed in a true knowledge representationlanguage

OWL (Web Ontology Language) = standardlanguage for ontologies


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Ontology

Ontologies enable a better communication

between Humans/MachinesOntologies standardize and formalize the meaningof words through concepts

An ontology is an explicit specification of a conceptualization .

People cant share knowledge if they do not speak a common language .


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^

Communication Principle

ReferentFormStands for

refers toevokes

Concept

Jaguar


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Views on Ontologies

Front-End

Back-End

TopicMaps

Extended ER-Models

Thesauri

Predicate Logic

Semantic Networks

Taxonomies

Ontologies

Navigation

Queries

Sharing of Know ledge

I nformation Retrieval

Query Expansion

Mediation Reasoning

Consistency CheckingEA I


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Taxonomy

Object

Person Topic Document

ResearcherStudent Semantics

OntologyDoctoral Student

Taxonomy := Segementation, classification and ordering of elementsinto a classification system according to their relationships betweeneach other

PhD Student F-Logic

Menu


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Thesaurus

Object



PhD StudentDoctoral Student

Terminology for specific domain Graph with primitives, 2 fixed relationships (similar, synonym) originate from bibliography

similarsynonym

OntologyF-Logic

Menu


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Topic Map

Object



PhD StudentDoctoral Student

knows described_in

writes

AffiliationTel

Topics (nodes), relationships and o ccurences (to documents) ISO-Standard typically for navigation- and visualisation

OntologyF-Logic

similarsynonym


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OntologyF-Logic

similar

OntologyF-Logic

similar

PhD StudentDoktoral Student

Ontology (in our sense)

Object


Tel

PhD StudentPhD Student

Semantics

knows described_in

writes

Affiliationdescribed_in is_about

knowsP writes D is_about T P T

DT T D

Rules

subTopicOf

Representation Language: Predicate Logic (F-Logic) Standards: RDF(S); coming up standard: OWL

ResearcherStudent

instance_of

is_a

is_a

is_aAffiliation

Affiliation

York Sure

AIFB+49 721 608 6592


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PhD Student AssProf

AcademicStaff

rdfs:subClassOfrdfs:subClassOf

cooperate_with

rdfs:rangerdfs:domainOntology

Steffen Staab

...

http://www.aifb.uni-karlsruhe.de/WBS/sst

Anno-tation

Siegfried

Handschuh

...

WebPage

http://www.aifb.uni-karlsruhe.de/WBS/shaURL

instance of

instanceof

Cooperate_with

Ontology & Metadata

Links have explicit meanings!


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Summary

The emergence of the Semantic Web

machine-processable information

Language stack: XML/RDF(S)/OWL Ontologies


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Introduction to Semantic Web

Checking your understanding

What are the semantic web layers?What is the key difference between thesemantic and syntactic web?

Documents

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