COST Action TU0902 Meeting: Web Processing Service (WPS) technologies for Integrated Assessment Modelling in Urban Areas

1. The Web Processing Service Standard
Benjamin Pross
2014-01-22
Workshop: WPS technologies for
Integrated Assessment Modelling in
Urban Areas

2. Geoprocessing
Raw Data
Value Added
Data Products
Information Products

3. Basic concepts
Process Model
control
Input Data
Sources
Process
Output Data
Sources

4. GIS & Geoprocessing
GIS
Processing control
Environment
Process
Input Data
Sources
Output Data
Sources

5. Web based Geoprocessing
Basic Goals:
Being able to share processes in a heterogeneous and
distributed computing environment, as to
• Share knowledge (white box processes)
• Reuse existing implementations
• Share computing capabilities
(e.g. from cloud and GRID environments)
2014-01-22 The WPS Standard
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6. OGC Standard
• OGC Web Processing Service (WPS)
– OGC Standard since late 2007 (Version 1.0.0)
http://www.opengeospatial.org/standards/wps
– Standardized service interface to publish and perform geospatial processes over
the web
• How to describe process offerings
• How to describe input/output parameters
• No processes are specified
– Supported Processes
• Simple geometric calculations (e.g. intersect algorithm)
• Complex simulation models (e.g. weather forecast)
• Interface to legacy software (e.g. GRASS GIS)
• ..
– Development of WPS 2.0 is in progress …
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7. Operations
GetCapabilities
GetCapabilities
WPS
Process 1
DescribeProcess
Process 2
Execute
Process n

8. GetCapabilities Request (http GET)
http://geoprocessing.demo.52north.org:8080/wps/WebProcessingService?
Request=GetCapabilities&
Service=WPS

9. Get Capabilities Response
Operations Metadata
2012-11-19 Spatial Information Infrastructures WS 2012/2013
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10. Get Capabilities Response
Process Offerings
2012-11-19 Spatial Information Infrastructures WS 2012/2013
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11. Operations
GetCapabilities
WPS
..
DescribeProcess
DescribeProcess
SimpleBuffer
Algorithm
Execute
..

12. DescribeProcess Request (http GET)
http://geoprocessing.demo.52north.org:8080/wps2/WebProcessingService?
Request=DescribeProcess&
identifier=org.n52.wps.server.algorithm.SimpleBufferAlgorithm
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13. DescribeProcess Response
Process description for „SimpleBuffer“
Data Inputs
Process Outputs
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14. DescribeProcess Response – DataInputs
a) the data to be buffered
Data Format GML 3.2.1 (default)
Further Formats supported
b) Parameter „buffer width“
Data format „double“
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15. DescribeProcess Response – ProcessOutputs
Resulting data (buffered)
Data Format GML 3.2.1 (default)
Further Formats supported
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16. Operations
GetCapabilities
WPS
..
DescribeProcess
SimpleBuffer
Algorithm
ExecuteProcess
Execute
..
DataInputs
ProcessOutputs

17. Example
WPS
Geometry
..
SimpleBuffer
Algorithm
Buffer Witdth
20
..
Geometry‘

18. Execute Request (http POST)
http://geoprocessing.demo.52north.org:8080/wps2/WebProcessingService
data to be buffered will be delivered by a WFS
buffer width = 20.0
Data Output: GML 3.1.1 document

19. WPS - Synchronous Execution
Sequence Diagram
Client
sends request
WPS
receives request
processes output
waits for response
sends results
receives response
and starts using it

20. WPS - Asynchronous Execution
(Push Model)
Sequence Diagram
Client
sends request
WPS
receives request
processes output
does something else..
receives response
and starts using it
sends results

21. WPS – Asynchronous Execution
(Pull Model)
Sequence Diagram
Client
WPS
sends request
receives request
reference
does something else..
sends status request
e.g. 33 %
does something else..
sends request for results
sends status
finalizes output
result
receives response
and starts using it
processes output
sends results

22. Asynchronous Execution
ExecuteProcess Request
store results
Provide status information
Provide output as a reference
to the stored results

23. Asynchronous Execution
ExecuteProcess Response (first status call)
Status: 33% completed

24. Asynchronous Execution
ExecuteProcess Response (second status call)
status: process successfully completed
Reference to process output

25. WPS Characteristics
• Web Processing Services
– Encapsulate any business logic (simple functions up to
complex models)
– Implement a web service profile for processing
Geospatial Data
– can be integrated into any application through
standardized web interfaces
– can be operated both within local or remote computing
environments

26. Challenges
• Interoperability problems
– Semantics, Encodings, Access constraints
• Discovery of WPS
• Ad hoc deployment of WPS in different target
environments
– Moving code
• Performant Processing of large datasets
– Dynamic allocation of ressources, streaming mechanisms

27. WPS - Use Cases
• I use a remote web processing service, because
– it is too expensive, to transfer it into my own computing
environment (technically too complex)
– It is tied to some data sources, which are available remotly
only (e.g. for geocoding)
– I don‘t have the capacity in my own computing
environment
– The provider offers a subscription model only
– I use it only occasionally, hence I dot want to bother with
the operating details

28. WPS implementations
• OGC lists 34 (WFS/WMS: several hundred)
• For information about Open Source WPS, check:
https://docs.google.com/presentation/d/1MJMLthdLjKwyyA3
Tf2b6VmyKJdcj8SULi-HoRpKTZRA/
• No reference implementations because no test suite
has been released
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29. Testing
• WPS 1.0 Compliance tests
– http://cite.opengeospatial.org/te2/about/wps/1.0.0/web/
– Currently do not match the abstract test suite (ATS) of the
standard
– Will not be released until they do
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30. WPS 2.0 Change Requests
• 34 official CRs
–
–
–
–
20 accepted (some with modifications)
3 postponed
10 rejected
1 withdrawn

31. WPS 2.0
•
•
•
•
•
•
Nested inputs
Devided into core and extensions
Status controlling
Better definition of WPS profiles
Better method of invoking processes synch/asynch
Better tests
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32. WPS 2.0
• Nested inputs
–
–
–
–
Specify one or more input types as „data type“ of an input
Established relations between inputs
Allows more structured inputs
Nesting level should be kept low
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33. WPS 2.0
• Devided into core and extensions
– Better extensibility
– Core concepts: Process model, service model
– New functionality can be introduced without changing
core concepts/schemas
– Open for different communication patterns like REST
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34. WPS 2.0
• Status controlling
– Introduce methods to pause/resume and cancel a process
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35. WPS 2.0
• Better definition of WPS profiles
– Clearly define what a process/service profile is
– Profiles are a way to improve interoperability
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36. WPS 2.0
• Better method of invoking processes synch/asynch
– Only one attribute has to be set
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37. Thanks!
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