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6 WPS overview
The specified Web Processing Service WPS provides client access to pre-programmed calculations andor computation models that operate on spatially referenced data. The
data required by the service can be delivered across a network, or available at the server. This data can use image data formats or data exchange standards such as Geography
Markup Language GML. The calculation can be as simple as subtracting one set of spatially referenced numbers from another e.g. determining the difference in influenza
cases between two different seasons, or as complicated as a global climate change model.
Enabling geospatial processing on the Internet requires the development of a wide variety web services to support atomic geospatial operations as well as sophisticated modelling
capabilities. It is important to standardize the way that these processes are called, in order to reduce amount of programming required, and to facilitate the implementation and
adoption of new services. WPS is intended to help OGC members to achieve these goals.
6.1 WPS Operations
The WPS interface specifies three operations that can be requested by a client and
performed by a WPS server, all mandatory implementation by all servers. Those operations are:
a GetCapabilities – This operation allows a client to request and receive back service
metadata or Capabilities documents that describe the abilities of the specific server implementation. The GetCapabilities operation provides the names and general
descriptions of each of the processes offered by a WPS instance. This operation also supports negotiation of the specification version being used for client-server
interactions.
b DescribeProcess – This operation allows a client to request and receive back detailed
information about the processes that can be run on the service instance, including the inputs required, their allowable formats, and the outputs that can be produced.
c Execute – This operation allows a client to run a specified process implemented by
the WPS, using provided input parameter values and returning the outputs produced. These operations have many similarities to other OGC Web Services, including the
WMS, WFS, and WCS. The interface aspects that are common with these other OWSs are specified in the OpenGIS
®
Web Services Common Implementation Specification [OGC 06-121r3]. Some of these common aspects are normatively referenced herein,
instead of being repeated in this specification. Figure 1 is a simple UML diagram summarizing the WPS interface. This class diagram
shows that the WPS interface class inherits the getCapabilities operation from the OGCWebService interface class, and adds the DescribeProcess and Execute operations.
This capitalization of names uses the OGCISO profile of UML. A more complete UML model of the WPS interface is provided in Annex C informative.
