Web Services and Geologic Data Interchange

Simon Cox

CSIRO Exploration & Mininghttp://www.em.csiro.au

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Outline

Web-hosted information services

Geospatial information services

Publishing geospatial information

Service chains

Web Services

HTTP is a lot more than web-pages

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Evolution of web-page delivery

Static webpages http://my.big.org/people/fred.html URL maps to disk-file

Dynamically generated webpages http://my.big.org/catalogue?item=358 URL maps to a parameterised procedure call Result still only accessible to humans

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Web services

Information services XML(?) packets of re-usable data

Computational services bigger parameter set

e.g. description of a finite element model!

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Parameterised request

Dynamically generated webpages http://my.big.org/catalogue?item=358 URL maps to a local procedure call with arguments

Each service encodes query differently unique UI typically have a single (browser-hosted) UI for each service tight integration is the norm

because of the requirement for advance agreement between client and service

Can we have looser integration? yes – if we can standardise query/response syntax this requires a standardised information-view

I.e. only possible within an information community

Geospatial Information Services

A big community …

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Open GIS® Consortium

Service implemented as a set of operations request-response message

pairs carried over http

Fine-grained

Important component of “Spatial Data Infrastructures”

NB – can be implemented on SOAP, but only http is required

Web Feature Service

Standard interface to geospatial data

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WFS in detail …

Standard request syntax: e.g. GetFeature

Standard response:

http://wfs.my.big.org&

SERVICE=WFS&

VERSION=1.0.0&

REQUEST=GetFeature&PROPERTYNAME=xmml:collarLocation,xmml:logs&TYPENAME=xmml:Borehole&BBOX=135.1,-34.0,135.2,-33.9

<gml:FeatureCollection gml:id=“C23"> <gml:boundedBy> … </gml:boundedBy> <gml:featureMembers> <xmml:Borehole gml:id="R456"> <xmml:collarLocation … /> <xmml:logs> … </xmml:logs> … </xmml:Borehole> … </gml:featureMembers></gml: FeatureCollection>

standard request keys FeatureCollection, using a GML application language

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WFS & Geography Markup Language

GetFeature request is cast in terms of the GML representation feature type, properties use element names from the GML

representation

Conformant WFS must provide a GML response other formats may be provided at discretion of service

provider e.g. shapefiles

WFS == “virtual GML view” of a data-store

http://wfs.my.big.org&

SERVICE=WFS&

VERSION=1.0.0&

REQUEST=GetFeature&PROPERTYNAME=xmml:collarLocation,xmml:logs&TYPENAME=xmml:Borehole&BBOX=135.1,-34.0,135.2,-33.9

Publishing Geospatial Information

Adding value to your data-store

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Private vs. public data models

WFS is a façade to a DB or GIS

WFSClient

WFSServer

Data-store normally organised for custodian’s requirements esp. maintenance

Published view should match community requirements

Responsibility for preparing data is on server-side

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Community language == interoperability

WFSClient

WFSServer

WFSClient

(data mining)

WFSClient/Server

WFSClient

(simulation)

WFSServer

Sensor

standard message new services can be added dynamically private agreements not required

(visualisation)

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Different views == different services?

Specimen

Au (ppm)

Cu-a (%) Cu-b (%) As (ppm) Sb (ppm)

ABC-123 1.23 3.45 4.23 0.5 0.34

Result/observation view: Cell

Feature view: Row

Coverage view: Column

Multiple interfaces to the same data-store each publishing a different “view” by

factoring the data using a different schema

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Adding more value

WFSClient

WFSServer

publish multiple views of same data

(visualisation) (measurements)

WFSClient

(visualisation)

WFSServer

(features)

WFSServer(coverages)

WFSClient

(visualisation)

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Deployment requirements

Develop GML Application Language(s) serialisation of community information model XMML + ?

WFS server-side software mapping from private to public data models on the server

Client applications desktop software must have WFS client back-end applets in standard portals browser-hosted applications

Middleware data-source catalogues, service registries, brokering SDI’s

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Alternatives

Publish an XML view of private data model less demanding on server - no-schema mapping on server

-> requires more work at the client

community interoperability based on standard “private” models (tables)

Ship Objects Corba, DCOM

tight binding, proprietary platform

.NET, Java-objects, SOAP

ArcIMS AXL mixes information, presentation, session state

Service chains?

Complex behaviour through composition of simple services

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Combining systems

Data Service

(Field Geologist)

Data Service

(Geophysical contractor)

Modelling service

(CAD)

Modelling service (FastFlo)

Data Service (Analytical

Lab)

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Data Service (Geological Survey)

Service binding

standard message new services can be added dynamically no private agreements

XMMLOver http,

email, filesystem

XMML - “Information bus”

Data Service

(In Situ sensor)

Data Service

(Field Geologist)

Data Service

(Geophysical contractor)

Portrayal service

Modelling service

(CAD)

Data Service (Analytical

Lab) Modelling service (FastFlo)

Modelling service

(Geochemists workbench)

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Take-home

Late binding of web-services requires standard request/response syntax

Standards for geospatial web-services are available from OGC

GML encoding of payload is required. This can 1. merely serialise the private data model

2. publish data according to a community language

Public/community language provides greater interoperability but imposes greater organisational challenge

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Questions?

http://xmml.arrc.csiro.au

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