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