Introduction to the OGC Web Processing Service WPS

1
Introduction to the OGC Web Processing Service
(WPS)

• GIP Meeting
• 20 April 2006
• Theodor Foerster

2
Contents

• Motivation
• WPS in detail
• Pitfalls
• Conclusion

3
Situation

• Spatial data is available on the web
• Through OGC web services (WFS, WCS)
• Network computational capacity available
• But users want to have information

4
Motivation

• Execute spatial processes as web services
• Platform independent
• Availability (worldwide 24/7)
• Maintenance
• Reusability
• ?Processing on the web is the next logical step

5
OGC WPS - history

• Founded by the CGDI (2004)
• Refined within an OGC interoperability experiment
• Discussion paper published in end 2005 under
  05-007r4 
• Awaiting adaptation for version 0.

6
Notion of the WPS

• Service communication based on HTTP and XML
• No limitations on certain types of processes
• No limitations on the data
• Supports raster and vector data
• Literal values (e.g. buffer size)

7
WPS operations

• GetCapabilities
• Service description
• Access description
• Brief process descriptions
• DescribeProcess
• Full process description
• Execute
• Process execution

8
WPS in action - Buffering
Client
WPS
http//geoserver8080/wps/WebProcessingService? RE
QUESTGetCapabilities SERVICEWPS
http//geoserver8080/wps/WebProcessingService? RE
QUESTDescribeProcess IdentifierBuffer SERVICE
WPS VERSION0.4.0
ltCapabilities version"0.4.0gt ltowsServiceIdenti
ficationgt ltowsTitle/gt ltowsAbstract/gt
ltowsKeywords/gt lt/owsServiceIdentificationgt lt
owsServiceProvider/gt ltowsServiceContact/gt
lt/owsServiceProvidergt ltowsOperationsMetadatagt
ltowsOperation name"Execute/gt
lt/owsOperationsMetadatagt ltProcessOfferingsgt ltP
rocessgt ltowsIdentifiergtBufferlt/owsIdentifiergt
lt/Processgt lt/ProcessOfferingsgt lt/Capabilitiesgt
ltExecuteResponsegt ltowsIdentifiergtBufferlt/owsIden
tifiergt ltStatus/gt ltDataInputsgt lt/DataInputsgt ltOu
tputDefinitionsgt lt/OutputDefinitionsgt ltProcessOu
tputsgt ltOutputgt ltowsIdentifiergtBufferResultlt/ows
Identifiergt ltComplexValue schema
schemaNSgt XML_Geometries lt/ComplexValuegt lt/Out
putgt lt/ProcessOutputsgt lt/ExecuteResponsegt
ltProcessDescriptionsgt ltProcessDescription
ltowsIdentifiergtBufferlt/owsIdentifiergt
ltDataInputsgt ltInputgt ltowsIdentifiergtgeometrylt
/owsIdentifiergt ltComplexData defaultSchemasche
maNS"/gt ltMinimumOccursgt1lt/MinimumOccursgt
lt/Inputgt ltInputgt ltowsIdentifiergtwidthlt/owsIde
ntifiergt ltLiteralDatagt ltowsDataType
owsreference"xsint"/gt ltProcessOutputsgt
ltOutputgt ltowsIdentifiergtBufferResultlt/owsIdenti
fiergt ltComplexOutput defaultSchemaschemaNS/gt
lt/ProcessDescriptionsgt
ltExecutegt ltowsIdentifiergtBufferlt/owsIdentifiergt
ltDataInputsgt ltInputgt ltowsIdentifiergtgeometry
lt/owsIdentifiergt ltComplexValue
schemaschemaNSgt XML_Geometries
lt/ComplexValuegt lt/Inputgt ltInputgt
ltowsIdentifiergtwidthlt/owsIdentifiergt
ltLiteralValuegt100lt/LiteralValuegt lt/Inputgt lt/DataIn
putsgt lt/Executegt
ltGetCapabilitiesgt request
ltGetCapabilitiesgt response
ltDescribeProcessgt request
ltDescribeProcessgt response
ltExecutegt request
ltExecutegt response
Network
Inspired by P. Schuts presentation at the OGC
TC Meeting in Huntsville 2006 WPS RFC responses
9
Additional Features

• Supports long-term processes by storing
• Handles drawback of HTTP
• Avoids recalculation
• Status of processes is callable
• Supports chaining (limited)
• For data retrieval processing
• Standardized error messages

10
Discovered pitfalls

• No advanced chaining available
• Semantic descriptions of processes are missing
• No sophisticated communication pattern
  incorporated
• No key advantage over SOAP

11
Implementation features - DEMO

• WPS identified as a basic module for
  generalization processing in the web
• Written in Java
• Published in 52n incubator
• Includes server and client (based on JUMP)
  implementation
• Based on open source APIs only
• Provides a pluggable mechanism

12
Conclusion

• WPS just evolving
• Many open issues
• Web Coverage Processing Service introduces
  additional ideas
• Will be part of ITCs 52n Working group on Geo
  Processing Service

13
Thanks

• Further information under
• www.incubator52n.de gt Processing
• Thanks for your attention!