Ontology Modules by Layering

1
Ontology Modules by Layering

• Facilitating Reuse in a Geographical Semantic Web
  Context

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Role of Semantic Web Ontology

• Conceptualise and convey a domain of interest.
• Agree and provide a vocabulary of terms to
  portray the hierarchical or taxonomic structure
  and the relationships and constraints.
• Serve as a vehicle to semantically link, or
  integrate, information across the Web.
• Facilitate information reuse by consistency of
  terms and fitness-for-purpose.

suitable for how it is going to be used
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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.

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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

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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.

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Ontology Mapping
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Informal specific Class Reuse

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

ltrdfRDF xmlns"http//www.livewiredg.myby.co.uk/
rdf/geo-layers/rail.owl" xmlnscyc"http//w
ww.cyc.com/2003/04/01/cyc" gt ltowlClass
rdfabout"cycTransportationCompany"/gt
ltowlClass rdfID"RailOperator"gt
ltrdfssubClassOf rdfresource"RailwayComponent"/
gt ltrdfssubClassOf rdfresource"cycTran
sportationCompany"/gt lt/owlClassgt ..

• Is this acceptable? How would an agent
  understand the Cyc context of the superclass of
  cycTransportationCompany

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Formalised specific Class Reuse
ltrdfRDF xmlnsglobal"http//www.livewiredg
.myby.co.uk/rdf/geo-layers/global.owl"
xmlnshttp//www.owl-ontologies.com/flight.owl
..gt ltowlClass rdfaboutglobalArtifact"/gt
ltowlClass rdfID"Helicopter"gt
ltrdfssubClassOfgt ltowlRestrictiongt
ltowlonPropertygt ltowlLinkProperty
rdfabout"hasForm"/gt lt/owlonPropertygt
ltowlsomeValuesFrom rdfresource"globalA
rtifact"/gt lt/owlRestrictiongt
lt/rdfssubClassOfgt lt/owlClassgt
ltowlLinkProperty rdfID"hasForm"gt
ltowlforeignOntology rdfresource"global"/gt
ltrdfsdomain rdfresource"Helicopter"/gt
ltrdfsrangegt ltowlforeignClass
rdfabout"globalArtifact"gt
ltowlforeignOntology rdfresource"global "/gt
lt/owlforeignClassgt lt/rdfsrangegt
lt/owlLinkPropertygt

• 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)

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Formalised specific Class Reuse

• SWOOP permits ontology partitioning (module
  extraction)

• partitioning generates same syntax as informal
  reuse example

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Class reuse by Ontology Import
Objective Map Rail Ontology class
RailOperator to Cyc Ontology class
TransportationCompany Action Import Opencyc
into Rail gt 6.8MB Effect adds 2843
classes 1256 properties 6331 instances Protégé
out of memory load time 1.5 to 7.5 mins
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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

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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.

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Efficient and Effective Context

• Efficient
• Minimise rework
• i.e. having to update a specification whereas
  stability contributes to reusability.
• Developing durable ontologies focus on
  permanence of terms and essentiality.
• Minimise redundancy
• avoiding duplication of terms reduce mappings.
• Minimise query complexity and processing
  overhead.
• Effective
• Using a consistent best practice approach
• Accurately and meaningfully describing concepts
  their relationships and constraints.
• Create small building blocks small ontological
  components serving as utility pieces.

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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.

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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)
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How could we quantify Import issues?

• Possible Import Inefficiency Metrics
• Filesize OA OB
• Classes OA OB
• Relevance OA OB
• Load Time OA (OA OB)
• Ontology Durability (or Permanence) OB
• How well specified is it, in terms of quality of
  constraints / definition?

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Ontology Permanence
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Ontology Permanence
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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 ..

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Transport Ontology

• Applications
• Passenger services
• Freight services
• Tourism
• Strategic route planning and development
• Supply industry
• Infrastructure planning
• Environment and Energy Waste, pollution, traffic
  volumes, resource consumption.
• Disaster management

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Land Transport
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Road-Rail Interchange
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Our Transportation Domain
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Transportation Domain Layers
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Railway sub-domain Conceptualisation
ContainerTerminal hasRole LoadingPoint UnloadingPoint
accessedVia FreightLine RailwayJunction
servedBy FreightOperator
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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

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Rail Transport Ontology
Q rename LevelCrossing ? RoadCrossing? But we
dont do roads in rail!
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Road Transport Ontology
Q rename LevelCrossing ? RailCrossing? But we
dont do rail in roads!
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Road-Rail Ontology Multimodal
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Development Issues

• Relegation and Elevation
• Declare parameters for ontology
• Scope of ontology development
• Purpose and Objectives
• Concept and Relation definitions

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Specifying Scope, Conceptualisation
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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