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Maintaining Ontologies forGeographical Information Retrieval

on the Web

Chris Jones, Alia Abdelmoty and Gaihua Fu

School of Computer ScienceCardiff University

http://www.geo-spirit.com

Spatially-aware Information Retrieval on the Internet

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Overview

• What is a geographical ontology

• Role of geo-ontology in spatial search engine

• Design considerations

• Design of SPIRIT geo-ontology

• Implementation of SPIRIT geo-ontology

• Future Work

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What is a Geographical Ontology?

Encodes knowledge of the terminology andstructure of geographic space

• Place names• Place types• Spatial footprints (geometric extent)• Spatial relationships between places

A global geo-ontology would representknowledge of all places on Earth

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Role of a geo-ontology in aspatially-aware search engine

• Query interpretation• System query formulation• Metadata extraction from documents• Relevance ranking

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Query interpretationAssume query of form:

Something Related-to SomewhereRelated-to = spatial relationship

e.g. in, near, north, X km from,…..

• Disambiguation of somewhere

• Feedback on spatial extent of SomewhereBased on analysis ofrelated-to Somewhere

• Recognition of geo-termsin free text query

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System Query Formulation

• Generate query footprint– from related-to + somewhere

or• Generate expanded set of geographical

query terms– Alternative names– Parent places, contained places from

hierarchy– Neighbouring places

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Document analysis / annotation

• Recognise place names and spatialrelationships in documents

• Generate document footprint(s) fromanalysis of geographical terminology

(for purposes of spatial indexing)• Generate geographical metadata for

document

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Geographical relevance ranking• Determine “distance” between geographical query

expression (related-to somewhere) andgeographical context of document.

• Compare query footprint with document footprint geometric distance/degree of overlap

Gets complicated with direction relations.

• Combine geographical relevance with thematicrelevance.

DQ

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SPIRIT architecture

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Design considerations

• Components of geo-ontology• Granularity of footprints• Integrity / consistency maintenance

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Components of geo-ontology• Place name

– Alternatives: Multilingual?, historical?• Place types

– Level of generalisation; single or multiple;– Place attributes

• Place location(Geometric footprint, +? address codes)Footprint :– Approximate or “exact”

• Point, Minimum Bounding Rectangle, area, line• Level of detail of line or area boundary

– ?multiple representations

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Design considerations (continued)• Coordinate system for footprint

– Latitude and longitude is global (but non-linear)• Spatial relationships between places

– topological (e.g. inside, contains, adjacent to..)– directional (e.g. angular bearings, north, south…)– proximal (distance X, “near”..)

Precomputation vs online computation– Every place has multiple relationships with every other

place too many to store all– Topological relationships can only be derived reliably

from high quality geometry– Directional and proximity relations degrade “gracefully”

with decreasing quality geometry

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The SPIRIT Geographical Ontology

Geographical FeatureGeographical Feature Type Spatial Relationship

Geographical Feature OntologyGeographical Feature Type Ontology

Geographical Ontology

Spatial Relationship Ontology

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Geographic Feature Types

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Geographic Feature (SPIRIT)

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Spatial Relationships between Features

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Integrity / consistency control

Type / instance level:E.g• Valid type• Mandatory properties present;• Value range constraints;• Cardinality constraints; etc

can use DAML-OIL validator

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Spatial consistency rule examplesIF Place A is inside Place B [spatial relationship]

then MBR(A) inside MBR(B) [geometric test][MBR = minimum bounding

rectangle for footprint ]

IF (A inside B)then not (A adjacent-to B) and not (A overlaps B)

IF (A inside B) and (B inside C) then (A inside C)

IF (A bigger-than B) then not (A inside B)

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Instance Database Management

• Queries to a search engine geo-ontologyneed to support spatial queries and spatialoperators

e.g. Inside, crossing, north-of, within-distance, area, length

Currently using Oracle Spatial which hasspatial indexing and some spatial querysupport

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Populating / building the geo-ontologySources of geo-data:• Gazetteers• Geographic thesauri (TGN)• Digital Maps

Footprints and Spatial relationships can be derivedfrom detailed digital map data;

--Containment relations derivable from someaddress and gazetteer data.

Problems of different feature type classifications,levels of detail, error, coordinate systems….

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Future work on SPIRIT geo-ontology

• What is appropriate level of geometric detail offootprints?– ? Multiresolution storage/access methods

• What is the best set of spatial relationships tostore (vs online computation) ?

• Validation of consistency of spatial relationships• Representation of imprecise places (e.g. “Midlands”,

“Borders”, “south of France”…..)• Data integration and distributed architectures for

global geo-ontologies