Querying a Geographic Database using an Ontology-Based Methodology Renata Viegas Valéria G. Soares [email protected] [email protected]

Querying a Geographic Database using an Ontology-

Based Methodology

Renata ViegasValéria G. Soares

[email protected]@ppgsc.ufrn.br

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Summary

• MotivationMotivation• System Architecture

• Semantic Layer

• Application Domain • Conclusion

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Motivation

• GIS are multidisciplinary systems• Geographic features are collected and

stored in GIS that were modeled based on a specific researcher vision.

• Current GIS must be able to solve the semantic interoperability.

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Motivation

• Semantic interoperability• A geographic feature could have more

than one description; • Interoperability based on the use of

ontologies as being a knowledge database type.

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Motivation

• Geographic Ontologies• A geographic ontology is a

conceptualization of a phenomenon or geographic object in the real world.

• Characteristics of geographic objects must be embodied to the ontology:• Location• Topology• Direction

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Geographic Ontologies

• Relationship through ontologies classes with typical geographic relationships

São José dosCampos

Campos do Jordão

JoãoPessoa

NortheastRegion

Near

Within

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Summary

• Motivation• System ArchitectureSystem Architecture

• Semantic Layer

• Application Domain • Conclusion

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System Architecture

• Our Problem:• Different professionals of distinct

research areas want to access the same GDB

• Our solution:• Based on geographic ontologies

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System Architecture

• The semantic layer intermediates the users’ queries with the geographic database• Each one of the users community could

interact with the system using only specific terms of its research area, and could receive its queries answers in an appropriate way.

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General System Architecture

Web Map Formulation

Application

Web Browser User Interface

Semantic LayerOWLOWL JENAJENA

PostgreSQL

PostGISGeographic Database

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Query Process

• The user query will be submitted• The system will recognize the used

terms.

• The next step is to look for the terms and concepts used in this query, in the users’ ontology• comparing the ontology with the GDB

ontology, looking for equivalent concepts.

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Query Process

QUERY USER

PHP

Java / Jena

QueryManagement

Users, Concepts, Terms

Database Request

Users Ontology

GDB Ontology

GDB

Semantic Layer

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Detailing the Semantic Layer• Step 1: Define the ontologies• Step 2: Bind definition between

the classes of the different ontologies• The result of this binding process is a

formal structure with expressions that show which terms of each ontology is related to others terms of another ontology.

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Detailing the Semantic Layer• Mapping synonyms classes

• Synonym classes are classes whose concepts have the same meaning, independent of their given names, that are related of the specific knowledge of each community.

• Ontologies Manipulation• We use Jena API to generate graphs RDF, which

is represented by resources, properties and literals;

• From the Jena API methods we can manipulate and compare the ontologies.

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Semantic Layer

Users Management

Module

Query Preparation

Module

Ontologies Management

Module

Comparative Module

QueryGeneration

Module

OWL

DictionaryGeneration

Module

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Semantic Layer Modules

• Users' Management Module• The first step to submit a query is to

inform which type of user wants to interact with the system

• The system will show a pay-define queries’ interface, with only specific terms of this type of users, based on the defined ontologies.

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• Ontologies’ Management Module• Activate ontologies

• User ontology and the ontology that represents the contents of the GDB

• The ontologies are stored in ontologies’ server, and are accessed through their URLs

• Methods of the Jena API will be used to construct the graphs (models) of the ontologies.

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• Query Preparation Module• This module will identify and store the

key terms of the query

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• Comparative Module• Search of similar terms in the ontologies

• The similarity is defined manually, based on the interviews with professionals of the different areas

• The OWL Tags• equivalentClass and sameAs

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• Comparative Module• The <owl:sameAs> tag is used when we

have different nomenclatures that refers to a same entity• A typical use of owl:sameAs is for ontologies’

unification, to say that two individuals classes, defined in different documents, are equals.

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• Comparative Module• Methods of the Jena API treat the

similarities binding classes of an ontology to another one• The getSameAs() method, by the

OntResource interface, is used to find the similar classes in the ontologies.

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• Query Generation Module• Mount the query that will be submitted

to the database• Use the terms found in the search for

the similarity, as well as the relationship used in the query interface.

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• Dictionary Generation Module• Mount a detailed text, with the key

terms of the query, supplying to the user descriptions about the geographic features involved in his queries.

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Summary

• Motivation• System Architecture

• Semantic Layer

• Application DomainApplication Domain • Conclusion

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Application: Coral Reef Domain• Geographic Domain: Coral Reefs• We have three different

communities: geologists, biologists and tourists• Development of three different

ontologies for each one of these communities.• The ontologies give support to the

construction of adaptable interfaces for each community.

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Developed Ontologies

• Geologist Ontology

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Developed Ontologies

• We also have developed ontology for the biologists community and tourists community

• The geologist ontology is the same of the geographic database ontology (GDB).

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Prototype Query Example

• Example: A tourist wants to “find the best area for dip in the sea nearby the coral reefs”

• Activated ontologies for this query: the geologist (Ogeo) and the tourist (Otur)

This information is not storedon our database…

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Prototype Query Example - Tourist• Steps:

• Look for the term dip in the sea on the tourist ontology• We defined in the Otur that a tourist could

dip in the sea around the floating boats or within the natural pools

dip in the sea

floating boat

natural pool

around

within

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• Look for an equivalent term on the geologist ontology• No similar class to “dip in the sea” could be

found in the Ogeo at this point

Prototype Query Example - Tourist

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Prototype Query Example - Tourist• Steps (Continue):

• Go down one more step on the tourist ontology• Verify if there is more information in the relationships

between classes or subclasses

• dip in the sea appears in the tourist ontology with properties that bind this class to other ones in the ontology

• The property “within” binds the class “dip in the sea” (domain) to the class “natural pool” (range)

• The property "surround", binds the class “dip in the sea” (domain) to the class “floating boats” (range)

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• the system will search now for classes similar to “natural pool” and “floating boats” on the geologist ontology• The class “floating boats” is defined on both

the tourist ontology Otur and the geologist ontology Ogeo

• The class “natural pool” is not found

floating boat

Reef anchor

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• The Comparative Module goes down one more step in the graph generated from the tourist ontology, looking for relationships between classes

• The relationship is found: “Natural pools” surround “Coral Reef”

naturalpool

coral reefsurround

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• The query that will be submitted to the GDB is: “show all the areas that surround the floating boats and the coral reefs bodies”

SELECT buffer (flutuante.flutuante_geom, 10) AS flutuante_geom,

buffer(corpo_coralineo.geom_cabeco, 10) AS geom_cabeco

FROM flutuante, corpo_coralineo

AS foo USING UNIQUE oid USING SRID = -1

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Results

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Results

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Prototype Query Example - Biologist• A biologist wants to know where

he could “find no consolidate substrates on the coral reef region”• Activated ontologies for this query: the

biologist (Obio) and the geologist (Ogeo)

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Prototype Query Example - Biologist• Steps:

• Look for the “no-consolidate substrate” class in the Obio ontology

• Look for class similarities on the definition of this class

• The class “no-consolidate substrate” in the biologist ontology has no similar class in any other ontology

• The comparative module will go down one more level, verifying whether the “no-consolidate substrate” class has some relationships with others classes or has sub-classes

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• The comparative module finds that the “no-consolidate substrate” class has sub-classes (relationship ISA) with the classes: “sand”, “gravel” and “mud”

no-consolidatesubstrate

sand gravel mud

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• Look for classes similar to “sand”, “gravel” and “mud” on the geologist ontology

Prototype Query Example - Biologist

no-consolidatesubstrate

sand gravel mud

sediment

sand

Benthic region

has

Obio Ogeo

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• The conceptual similarity is found• The Query Generator Module will

construct this following SQL query clause

SELECT geom_areia AS geom_areia, geom_lama AS geom_lama, geom_cascalho AS geom_cascalhoFROM areia, cascalho, lamaAS foo USING UNIQUE oid USING SRID = -1

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Results

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Results

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Summary

• Motivation• System Architecture

•Semantic Layer• Application Domain • ConclusionConclusion

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Conclusions

• Summary of Contributions:• Development of the ontologies for the

coral reef domain, based on three points of view of different communities: the geologists community, the biologists and the tourists• We choose a natural environment of coral

reefs because no other proposal makes use of semantic terms with this kind of geographic databases.

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Conclusions

• Summary of Contributions:• An ontology-based mechanism allows

different users’ communities, through geographic ontologies, to access the same database, without knowing its internal structure• With only one database implementation and

the definition of different communities’ ontologies, anyone can search the database, in a transparent way, using a specific interface.

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Conclusions

• Summary of Contributions:• A Framework for this mechanism

• The Semantic Layer can be adapted to any spatial domain of multidisciplinary interest.

• Future Work• Extend this Architecture

• Bind the classes automatically• Define ranking of similarities between the

classes.

Querying a Geographic Database using an Ontology-

Based Methodology

Renata ViegasValéria G. Soares

[email protected]@ppgsc.ufrn.br

Documents

Querying a Geographic Database using an Ontology-Based Methodology Renata Viegas Valéria G. Soares [email protected] [email protected]