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Local Spatial Data InfrastruturesBased on a Service-Oriented Architecture

Clodoveu DavisLeonardo Lacerda Alves

PUC Minas

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Introduction There is demand for GIS in large

computational environments, with a large number of users, spread over numerous locations, and high volumes of data

Factors: The fast development of networking

technology and the Internet The success of Web-based GIS The wide applicability of mobile and

ubiquitous computing

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Introduction

Many challenges arise when someone tries to share (geographic) information: Data format/data structure issues Data quality issues Content issues Semantics

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Introduction

Early solutions included Data translation tools Offline data replication “Negotiated” semantics through

(poor) metadata This led to intensive data

redundancy and numerous updating/synchronization problems

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Introduction Data sharing and exchange among

several organizations is hard to achieve

It involves at least A lot of political negotiation Agreements on standards Agreements on costs and cost sharing Agreements on maintenance ....

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Introduction The impact of such data exchange and sharing

efforts is very positive We need technology that can make such efforts

pay off Easier data access

Semantics Less maintenance and synchronization issues

Semantics Data usage directly from the source, without translation

or replication More applications

Free access to base maps Public services Value-added services

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Our proposal Extension of the concept of Spatial

Data Infrastructures (SDI) to local data and applications

Definition of the architecture and creation of a local, intra-organizational, service-oriented local SDI Most SDIs are national or regional in

scope Service-oriented architectures help with

interoperability issues

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A Brief History of GeoData Sharing

Spatial data transfer standards Spatial data clearinghouses Spatial data infrastructures Geoportals

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Early GIS

Dataset creation was really expensive and complex

Redundant efforts were commonplace

Potential data providers were late adopters of GIS technology

Incipient market of data conversion services

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Spatial Data Transfer Standards

Only helpful with syntactic problems Data sharing requires

An offline semantics agreement, plus Select-export-copy-translate-import,

plus Some luck

There are a number of proposed standards, but none has achieved widespread acceptance

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Spatial Data Clearinghouses

SD Clearinghouses have been described as sites through which a number of services related to spatial data can be accessed

The emphasis on services is recent: this concept has been initially implemented as a means to obtain “off-the-shelf” data

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Spatial Data Clearinghouses

A 2004 study on national SDCs showed that there is a growing dissatisfaction from users as to the functional capabilities available

The study indicates that the focus should be user- or application-oriented, instead of data-oriented

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Spatial Data Infrastructures Evolution from the clearinghouse

perspective “Infrastructure” implies that there should

be some sort of coordination for policy formulation and implementation

US definition (NSDI): “technologies, policies, and people necessary

to promote sharing of geospatial data through all levels of government, the private and non-profit sectors, and the academic community”

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Spatial Data Infrastructures

SDI objectives are similar to the ones pertaining to other kinds of infrastructure Fostering economic development by

means of a range of publicly-available, multiple-use goods or services

This does not mean that the services are free of charge: do not confuse “publicly- available” with “government-supported”

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Spatial Data Infrastructures

SDIs should Provide standardized access to data Have multiple participants, in the role

of information services providers and/or users

Have a broad thematic scope

Facilitate data sharing

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Spatial Data Infrastructures

Widespread adoption of Internet-based tools allowed the creation of Web portals to multiple geographic information sources Geoportals

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Geoportals

Geoportal Web site that presents an entry point

to geographic content on the Web Includes tools for

The discovery of information sources and content

Online access to Web-based applications

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SDI vs. Geoportal SDI

Confluence of several different geodata providers

Access through specific Web services Requires a repository or catalog of available

services Metadata

Usage by applications Geoportal

An SDI encapsulated by a human-computer interface

Should be considered a component of an SDI

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HumanUser

Geoportal

Search Discovery

GI Service Provider

Da

tare

spon

se

Ser

vice

s re

ques

t

Ser

vice

s re

ques

t

Dat

a re

spon

se

SDI

Pub

lish

met

adat

aServices and DataCatalog

Catalog Web

Service

Software Client

Dat

are

spon

seS

ervi

ces

requ

est

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Service-based Distributed Systems Architecture

Service-oriented architecture (SOA) Involves service providers, service

aggegators and service users Users may be human or software

clients Available services are listed in

directories by providers Aggregators design compositions of

rules based on primary services

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SOA

Web Service User

Web Service Provider

Web Services Directory

Discover / Select

Bind

Publish

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OWS vs WS There is currently some confusion

between OGC Web services (OWS) and W3C Web services (WS) OWS do not necessarily use the usual

W3C standards, including SOAP and WSDL Instead of UDDI, OWS propose the use of

catalog services OWS have a particular interface for

binding OWS use GML, and not plain XML

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OWS vs WS The OGC has specified a range of basic

Web services Web Feature Service Web Coverage Service Web Map Service Web Gazetteer Service Web Registry Service/OpenGIS Catalog

Service Web Coordinate Transformation Service Web Terrain Service

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Local SDI

Most SDI development efforts focus on the usual activities of national mapping agencies, as the usual providers of basic mapping data

The richness of local GIS applications indicates that SDIs focused on local data can also be important

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Local SDI Motivation

The large number of actors involved in spatial activities in urban areas

The wide variety and high detail level of information classes involved in urban applications

The potential for fostering new applications on commercially interesting subjects

Location-based services Personal routing Convenience shopping ...

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Local SDI

A local SDI and an urban GIS are very different SDI: widely-available, general-use

data, accessible through services GIS: organizational tool, built and

operated around a definite set of goals

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Local SDI

An urban GIS (maintained by the local government) may or may not become an SDI, depending on how freely the government distributes its information, and on how well other urban data providers are integrated in the maintenance effort

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Users

Web Services

University Federal agencyNGO State agency Local Gov Commercial provider

Met

adat

a on

da

ta a

nd

serv

ices

Services Registry XML

Geographic Information Providers

XML / GML

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Services of Interest for a Local SDI Basemap Personal location Geocoding/address recognition and

location Routing service Public transportation system Public services Private services Emergency services

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Services of Interest for a Local SDI The proposed services are rather

different from the ones specified for NSDIs

It should be possible to chain these services to generate more complete or integrated services Value-added commercial services based on

public data Public information of commercial interest

available through a fee Coordination of efforts during emergencies

and natural disasters

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Conclusions and Future Work

This is a work in progress We are currently working to create

a prototyping environment for Web services and SOA

An undergoing project on geocoding is being reconfigured to work under Web services

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Conclusions and Future Work Our goals include

Develop a better understanding of the SDI approach

Including performance, privacy, and security concerns

Develop a method for the design and implementation of WS/OWS for the SDI

Design means to publish metadata on services Study the architectural possibilities for

chained Web services Mobile GIS applications

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clodoveu@pucminas.brleonardo@lacerda.eti.br