Efficient Reuse of

looneyvillebiologistInternet and Web Development

Oct 21, 2013 (3 years and 7 months ago)

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The Semantic Web

and


Efficient Reuse of

Ontology Modules



MSc CO3701 Advanced Database Systems Research Topics


5 March 2008

David George, Dept. Computing, UCLan.

What is the Semantic Web?


A project aimed to make web pages
machine understandable
.



An extension of the current Web, … information given well
-
defined
meaning, …enabling computers and people to work in co
-
operation


(Berners
-
Lee et al, 2001)


A universal medium for information
integration

and
exchange
.


Uses Ontology


a formal domain representation that specifies
the meaning (
semantics
) of a domain or context.


We have the Web: a Global Information Space

Some current Web statistics



Approx. 70m web sites



Circa 15
-
20 billion pages (files)


Semantic Web share



0.004% usable Semantic Web files (800k)



0.00005% are Ontology files (10k)

Swoogle

Visualising the Semantic Web?

DE BRUIJN, J. (2003)
Using Ontologies
-

Enabling Knowledge Sharing and Reuse on the Semantic Web

[online]. DERI


Digital
Enterprise Research Institute. Available from:
http://www.deri.ie/publications/techpapers/documents/DERI
-
TR
-
2003
-
10
-
29.pdf
.
[Accessed 4 March 2008].

What is an Ontology?



“An Ontology is a formal, explicit specification of a shared
conceptualization”


(Gruber, 1993 & Borst, 1997).



constraints

on those relationships

makesSolarFlightTo

Moon

moonRocket

[ hasWeight = 100t ]

Every

moonRocket makesSolarFlightTo
only

Moon


Ontology specifies the vocabulary of a “
Domain




concepts

and their attributes



relationships

between concepts

What does an Ontology look like?

Biblio
-
Thing

Document

Book

Periodical
-
Publication

Journal

Magazine

Newspaper

Thesis

Doctoral
-
Thesis

Master
-
Thesis

Agent

Person

Author

Organisation

Publisher

University


A useful source for ontologies:

http://protegewiki.stanford.edu/index.php/Protege_Ontology_Library

An example of a Bibliographic Ontology

Semantic Web Technologies


Based on “XML
-
based”
RDF

(Resource Description Framework)
and
OWL

Ontology

languages (W3C, 2004).


OWL has foundations in Description Logics (DL)


decidable fragments of First Order Logic.


OWL can be reasoned with using DIG Reasoners (short for DL
Implementation Group)


Reasoner can establish subclass/superclass relationship of concept.


Can infer equivalence, transitivity of classes and relations class


Can determine ontology consistency.



Built on
subject
,
predicate
,
object

triples [a statement]



A statement may say:
<student> <lastname>

is
<George>



For example:

RDF (Resource Description Framework)


subject

object

predicate

Uses for the Semantic Web?


Data integration e.g. integrating heterogeneous database
structures/schemas and semantics?



Annotation of Internet resources i.e. Web pages


to assist Web
crawler/robot/spiders. Semantic (Shadow) Web?



Support Search Engine queries


to improve relevance of retrieval
hits?



Facilitation of understanding between e
-
government portal
terminology and users natural language?

Typical Search Engine Query

Search Hits


S
e
m
a
n
tic

S
e
m
a
n
tic

KB

DB

a

a

a

a

a

a

a

a

Ontology Development

One large ontology or many?


Complexity of ontology specification makes it impractical.


How do you describe the world!!


Ontologies conceptualised by domain specialists.


Applications will require ontology
integration

capability.


Fulfils
Reuse

capability


Risk of
redundancy

through overlapping class sets.

So let’s consider
Land Transport

….

Our Transport Ontology

Possible Application uses:


Public transport
services


Commercial Freight
services


Linking

towns
and

cities
by

road
and

rail



We may need to consider
bringing together

road, rail and
population centre
ontologies.

But first, why not use an existing ontology?


Reuse via Ontology imports


E.g. if
OTN
1

is imported: what do we
see?


Small Ontology but describes multiple
sub
-
domains



Potential redundancy


Vulnerability to change


How relevant are they?


Only for an application that uses
ALL concepts

1

OTN

-

Ontology of Transportation Networks (Lorenz et al, 2005)


Our Land Transport scenario

The Channel Tunnel Rail Link (CTRL) is the international connection and, whilst essentially a single mode of transport, it
also interfaces with road transport. Other road
-
rail interfaces, not shown, might be level crossings and transport
interchanges.































Cheriton Channel Tunnel Terminal © OS Get
-
a
-
Map.

The multimodal element of CTRL operation is the Channel Tunnel transport interchange in Cheriton, accessed by road and
rail for its drive
-
on drive
-
off service

Let us assume the Rail domain contains various concept and relationship statements:



RailRoute startsFrom RailwayStation


RailwayStation locatedIn City


RailRoute hasRailComponent RailwayLine


RailwayLine meetsObstacle LevelCrossing


LevelCrossing intersectionBetween (RailwayLine


Highway)


RailwayStation accessedVia Highway


These statements are combined to form the Rail model

NB: certain concepts (
City
,
Highway
) are likely to be logical concepts in Road and
PopGroup sub
-
domains.

For the Road module fragment we have described that:



-

a highway provides access to a city and transport facility


-

a drive
-
on/drive
-
off facility is available at a transport interchange


-

our highway encounters a railway (level crossing)


-

various operators use the transport interchange.






























Again, for the Road domain we see that certain concepts (
City
,
Highway
)
replicate the Rail sub
-
domain.


The PopGroup sub
-
domain shows various travel relationships including
City

and
Town
, and the
DormitoryTownRole

the latter may fulfil.



























PopGroup would specify how concepts might be accessed from each other, again
resulting in similar relationships as Rail and Road.

LandTransport Ontology

We have three sub
-
domains created as modules or
contexts
.


These Contexts might now be logically clustered within a
multimodal
LandTransport application ontology, itself containing
general

transport
concepts:
TransportInterchange
,
TransportOperator

and
various transport roles.

Import implications?: Road, Rail, PopGroup modules into
LandTransport

Concept duplication and redundancy, e.g:
rail:RailwayStation
,
road:RailwayStation

and
pop:RailwayStation
; also between
rail:City
,
road:City

and
pop:City
.

We see:

Relation duplications, such as
rail:encountersHazard

and
road:encountersHazard
.

Land Transport + Contexts

So How do we develop “Geo
-
Modules”


Need to “de
-
integrate” to allow low
-
cost integration


Aim towards “effectively” disjoint domains


Deliver by removing concept duplication between modules


redundancy


Need to promote/relegate
multi or single
-
context

concepts
and relations

Visualising de
-
integration of domains

This process of semantic
-
layering represents a conceptual
process of module de
-
integration to make distinctions.


We reduce each sub
-
domain to a single context, e.g. the Rail
model is depicted (next page).

Rail is now stated more formally:


Let a domain ontology
O

that contains
concepts

C
,
relations

R

and has a
domain
context

CT

be a set
O =
<<
C
(1,,,n)
>
,
<
R
(1,,,n)
>
, CT
>
.


The multi sub
-
domain ontology set can then be represented as:

O =
<<(
C
P1,,,
C
Pn
),
(
C
S1,,,
C
Sn
)>
,
<(
R
P1,,,
R
Pn
),
(
R
S1,,,
R
Sn
)>
,
<
CT
P
,
(
CT
S1,,,
CT
Sn
)>>

Transportation Domain
Layers

In each sub
-
domain we differentiate between the
primary

concepts and relations and
secondary
. Any secondary concepts and relations are removed to be primary concepts
and relations in their own contexts.

Comparisons show a reduction in classes (from 17 to 11) and in relations (34 to 20)


End