Ontology Modules by Layering

Facilitating Reuse in a Geographical Semantic Web Context

Ontology and Integration

• A Semantic Web lift-off requires critical mass and/via wider acceptance.

• Ontology development still at a stage where little interchange between organisations?

• Ontology Reuse is a key Integration benefit.

• Merger, Alignment and Mapping complexity issues when considering Integration.

Ontology and Integration

• Developer reluctance – easier to re-invent own dedicated local ontology specification than reuse.

• Reuse of an external ontology will likely result in descriptive and structural irrelevances.

• A move towards smaller component ontology modules – that can then be improvised as required – may encourage wider usage/take-up

Ontology Integration

Possible Ontology [ On ] Objectives

1. Merger: OA + OB → OC

2. Alignment: OA ≡ OB ≡ OC

3. Mapping: a virtual integration where OA, OB and OC concepts are semantically related.

Methods– 1 and 2 are achieved by rewriting (reformulation).

– Original ontologies are subsumed or made consistent (respectively).

– 3 is achieved by mappings between concepts of imported ontologies. A, B and C endure autonomously.

– Ontology Reuse, in this presentation, refers to 3: Mapping.

“Informal” specific Class Reuse

• Using namespace declaration to explicitly specify a single external concept, e.g.

<rdf:RDF xmlns="http://www.livewiredg.myby.co.uk/rdf/geo-layers/rail.owl#" xmlns:cyc="http://www.cyc.com/2003/04/01/cyc#" > <owl:Class rdf:about="&cyc;TransportationCompany"/> <owl:Class rdf:ID="RailOperator"> <rdfs:subClassOf rdf:resource="#RailwayComponent"/> <rdfs:subClassOf rdf:resource="&cyc;TransportationCompany"/> </owl:Class> ……..

<rdf:RDF xmlns="http://www.livewiredg.myby.co.uk/rdf/geo-layers/rail.owl#" xmlns:cyc="http://www.cyc.com/2003/04/01/cyc#" > <owl:Class rdf:about="&cyc;TransportationCompany"/> <owl:Class rdf:ID="RailOperator"> <rdfs:subClassOf rdf:resource="#RailwayComponent"/> <rdfs:subClassOf rdf:resource="&cyc;TransportationCompany"/> </owl:Class> ……..

• Is this acceptable? How would an agent understand the Cyc context of the superclass of “cyc:TransportationCompany”

“Formalised” specific Class Reuse

E-Connections

• Representation and reasoning with foreign ontologies (Grau et al, 2005)

• Allows specific concept linking. Few tools available e.g. SWOOP (OWL Ontology Editor)

<rdf:RDF xmlns:global="http://www.livewiredg.myby.co.uk/rdf/geo-layers/global.owl#" xmlns=http://www.owl-ontologies.com/flight.owl# ……..>

<owl:Class rdf:about=“&global;Artifact"/> <owl:Class rdf:ID="Helicopter"> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty> <owl:LinkProperty rdf:about="#hasForm"/> </owl:onProperty> <owl:someValuesFrom rdf:resource="&global;Artifact"/> </owl:Restriction> </rdfs:subClassOf> </owl:Class>

<owl:LinkProperty rdf:ID="hasForm"> <owl:foreignOntology rdf:resource="&global;"/> <rdfs:domain rdf:resource="#Helicopter"/> <rdfs:range> <owl:foreignClass rdf:about="&global;Artifact"> <owl:foreignOntology rdf:resource="&global; "/> </owl:foreignClass> </rdfs:range> </owl:LinkProperty>

<rdf:RDF xmlns:global="http://www.livewiredg.myby.co.uk/rdf/geo-layers/global.owl#" xmlns=http://www.owl-ontologies.com/flight.owl# ……..>

<owl:Class rdf:about=“&global;Artifact"/> <owl:Class rdf:ID="Helicopter"> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty> <owl:LinkProperty rdf:about="#hasForm"/> </owl:onProperty> <owl:someValuesFrom rdf:resource="&global;Artifact"/> </owl:Restriction> </rdfs:subClassOf> </owl:Class>

<owl:LinkProperty rdf:ID="hasForm"> <owl:foreignOntology rdf:resource="&global;"/> <rdfs:domain rdf:resource="#Helicopter"/> <rdfs:range> <owl:foreignClass rdf:about="&global;Artifact"> <owl:foreignOntology rdf:resource="&global; "/> </owl:foreignClass> </rdfs:range> </owl:LinkProperty>

“Formalised” specific Class Reuse

• partitioning generates same syntax as “informal reuse” example

• SWOOP permits ontology partitioning (module extraction)

Class reuse by Ontology Import

Objective:

Map Rail Ontology class “RailOperator” to Cyc Ontology class “TransportationCompany”

Action:

Import Opencyc into Rail > 6.8MB

Effect:

adds 2843 classes1256 properties6331 instancesProtégé “out of memory”load time 1.5 to 7.5 mins

Alternative Reuse approach?

• Consider the way Ontologies structured?

• Break down domain ontologies into sub-components: effectively domain “sub-classes” (Layers / modules)

• How to demonstrate?

• Can be demonstrated using Geographical context

Why consider Geography Context?

• Geographical concepts interact with virtually every aspect of daily life.

• Geographical elements form a major part of information management systems.

• Geographical ontologies offer a logical vehicle, to examine how Web semantics can be specified efficiently and effectively.

PC and Ontology Analogy

• Adding a component to a PC

– To enhance our own PC, we would not buy a complete PC with all components specified,

– It would require dismantling and refitting – some parts may not be compatible

– Result: additional, unnecessary and costly extra work.

• Accepted Protocol

– Build our requirement from small, interchangeable components

– Preferably with multiple PC compatibility.

Ontological Comparison

• Ontology Reuse - Imports– should there be a similar approach?– E.g. if OTN 1 is imported: what do we

see?– Ontology much smaller than Cyc, but …

• 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)

Ontology Permanence

Fixed Concepts

Variable Concepts

Ontology Permanence

Fixed Classes

Variable Classes

Transport Ontology

• How might we approach developing a modular ontology set?

• Previously discussed considering “map layers”

• No scientific justification for this - but offers a conceptual discipline that could be exploited for our purposes

• Example: consider a “LandTransport” ontology …..

Land Transport

multimodal

single-mode ?

Road-Rail Interchange

Our Transportation Domain

M67M6

A6

Transportation Domain Layers

M67M6

A6

Railway sub-domain Conceptualisation

ContainerTerminal hasRole LoadingPoint

UnloadingPoint

accessedVia FreightLine

RailwayJunction

servedBy FreightOperator

Developing Layers

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

• We are aiming towards “effectively” disjoint domains

• Achieved by removing concept redundancy – potential duplication

• Need to promote/relegate concepts and relations

• Represents a separation of Form and Function both within and between ontology modules

• e.g. see …… TransportInterchange, LevelCrossing

Rail Transport Ontology

Road domain

Q: rename LevelCrossing → RoadCrossing?

But we don’t do roads in rail!

Road Transport Ontology

Rail domain

Q: rename LevelCrossing → RailCrossing?

But we don’t do rail in roads!

Road-Rail Ontology: Multimodal

DriveOn-DriveOffRole

TransportInterchange

ChannelTunnel Terminal

LevelCrossing

Benefits and Issues

• Advantages– Small is manageable– Select only required building block modules– Independent therefore less vulnerable to change– Change is isolated to the module and subsuming

domain?

• Disadvantages– Increased mappings?– Needs to be examined