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Workflow Enactment of Grid-Enabled Geospatial Web Services

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Presentation on theme: "Workflow Enactment of Grid-Enabled Geospatial Web Services"— Presentation transcript:

1 Workflow Enactment of Grid-Enabled Geospatial Web Services
Gobe Hobona, David Fairbairn, Philip James

2 Overview Background OGC Web Services Workflow Enactment
SAW-GEO Architecture User interface – Geoportal Conclusions

3 Background Open Geospatial Consortium (OGC) ISO19119 and OGSA
JISC Grid/OGC Collision Programme Security : SEE-GEO Workflow : SAW-GEO OGC Interoperability Experiments (OWS-4)

4 OGC Web Services Web Feature Services (WFS) Web Map Services (WMS)
Disseminates vector geospatial data Web Map Services (WMS) Renders portrayals/visualisations Web Coverage Services (WCS) Disseminates raster geospatial data Web Processing Services (WPS) Runs geocomputational models or geospatial operations on user-supplied datasets

5 Sample OWS Request Messages
<wfs:GetFeature service="WFS" version="1.0.0" outputFormat="GML2" xmlns:topp=" xmlns:wfs=" xmlns:ogc=" xmlns:gml=" xmlns:xsi=" xsi:schemaLocation=" <wfs:Query typeName="topp:states"> <wfs:PropertyName>topp:STATE_NAME</wfs:PropertyName> <wfs:PropertyName>topp:PERSONS</wfs:PropertyName> <ogc:Filter> <ogc:BBOX> <ogc:PropertyName>the_geom</ogc:PropertyName> <gml:Box srsName=" <gml:coordinates> , , </gml:coordinates> </gml:Box> </ogc:BBOX> </ogc:Filter> </wfs:Query> </wfs:GetFeature>

6 Sample OWS Response Messages
</gml:featureMember> <gml:featureMember> <topp:states fid="states.40"> <topp:the_geom> <gml:MultiPolygon srsName=" <gml:polygonMember> <gml:Polygon> <gml:outerBoundaryIs> <gml:LinearRing> <gml:coordinates decimal="." cs="," ts=" "> , , …… , , , , </gml:coordinates> </gml:LinearRing> </gml:outerBoundaryIs> </gml:Polygon> </gml:polygonMember> </gml:MultiPolygon> </topp:the_geom> <topp:STATE_NAME>Pennsylvania</topp:STATE_NAME> <topp:PERSONS> E7</topp:PERSONS> </topp:states> …. NCOLS 522 NROWS 300 XLLCENTER YLLCENTER CELLSIZE E-4 NODATA_VALUE

7 Grid-enabling OWS SOAP-based proxy service
Created from OGC XML schemas (XSD) Requests create temporary datasets Resource management at two levels Temporary datasets managed by proxy service Persistent data managed through OWS e.g. WFS-T Security limitations OWS currently do not offer message encryption Approach to wrap OWS in firewall and allow external access only through proxy service

8 Geospatial Data is Very Large
Vector data Thousands of coordinates Multiple dimensions Raster data Thousands of pixels (very high resolution) Multispectral imagery (200+ band imagery) Solution Pass data by URL references and get client to stream data in

9 Load Experiment

10 Workflow Enactment Recognised by both ISO19119 and OGSA
Several options for workflow enactment SCUFL, BPEL, Keppler etc Selected BPEL because OASIS Standard, i.e. WS-BPEL 2.0 Multi-vendor support including IBM, Sun Microsystems, ActiveEndpoints, Oracle etc Availability of open source enactors In orchestration, which is usually used in private business processes, a central process (which can be another Web service) takes control of the involved Web services and coordinates the execution of different operations on the Web services involved in the operation. The involved Web services do not "know" (and do not need to know) that they are involved in a composition process and that they are taking part in a higher-level business process. Only the central coordinator of the orchestration is aware of this goal, so the orchestration is centralized with explicit definitions of operations and the order of invocation of Web services Choreography, in contrast, does not rely on a central coordinator. Rather, each Web service involved in the choreography knows exactly when to execute its operations and with whom to interact. Choreography is a collaborative effort focusing on the exchange of messages in public business processes. All participants in the choreography need to be aware of the business process, operations to execute, messages to exchange, and the timing of message exchanges

11 WS-BPEL Overview Based on Activities Variables Conditionals Loops
Basic or Structured Variables Declaration Assignment Conditionals Loops Fault handlers

12 An Example Geospatial Workflow
WPS 1 Generalise WFS Workflow Enactor client WPS 2 Clip Based on OGC OWS-4 GeoProcessing Workflow Scenario

13 Possible Applications for Geo-Workflows
Emergency Management Where each activity depends on the result of a previous activity Geographic modelling Where several steps are needed before a final model is produced e.g. ESRI Model Builder Climate Change scenarios Where a number of possible routes for workflows are possible depending on the state of certain variables

14 Components Geoserver 52North WPS ActiveBPEL Open Source Engine
Globus Toolkit (GT4) …or Apache Axis 2

15 SAW-GEO Architecture

16 Geoportal User Workflow Monitoring Browser-based BPEL Upload
Hot deployment AJAX-based SOAP client Workflow Monitoring ActiveBPEL Admin Console Offers views of deployed processes Exports list of available services to SOAP client as XML Red font: Developed for SAW-GEO

17 ActiveBPEL Workflow Engine

18 Discussion Importing OGC XSD into SOAP services offered high interoperability However, variations in how tiers interpreted the XSD varying namespaces cyclic imports Necessary to generate faults at SOAP tier from faults at OGC tiers, because BPEL can handle SOAP faults Variations in GML between workflow nodes, potentially requiring ‘shim services’ when chaining OWS

19 Conclusions SOAP wrappers needed for Grid-enabling OGC web services
OGC XSD appropriate for creating SOAP wrappers BPEL can support Grid-enabled OGC web services Geospatial data best passed through URL references to avoid overwhelming the workflow enactor

20 Future Work Experimental deployment on the Belfast e-Science Centre (BeSC) DEBUT system Investigate deployment on upcoming NGS GT4 infrastructure User Evaluation (November-December 2007) Volunteers needed – Please register on the website Integration with SEE-GEO

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