Download - Ontology Modules by Layering
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