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 • Merger: OA + OB→ OC • Alignment: OA≡ OB≡ OC • 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> …….. • 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>
“Formalised” specific Class Reuse • SWOOP permits ontology partitioning (module extraction) • partitioning generates same syntax as “informal reuse” example
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 classes 1256 properties 6331 instances Protégé “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 • Multiple sub-domains • potential redundancy • vulnerability to change • How relevant are they? • 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 … • Only for an application that uses ALL concepts 1OTN - Ontology of Transportation Networks (Lorenz et al, 2005)
Fixed Concepts Variable Concepts Ontology Permanence
Fixed Classes Variable Classes Ontology Permanence
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 …..
multimodal single-mode ? Land Transport
M6 M67 A6 Our Transportation Domain
M6 M67 A6 Transportation Domain Layers
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
Road domain Rail Transport Ontology Q: rename LevelCrossing → RoadCrossing? But we don’t do roads in rail!
Rail domain Road Transport Ontology Q: rename LevelCrossing → RailCrossing? But we don’t do rail in roads!
ChannelTunnel Terminal DriveOn-DriveOffRole LevelCrossing TransportInterchange Road-Rail Ontology: Multimodal
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