Web Processing Service

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An OGC Web Processing Service (WPS) is a Web Service that takes a defined set of inputs, applies a calculation, and produces a defined set of outputs. WPS is designed to work with spatially referenced data but can be used with other kinds of data. WPS is a generic Web Service in that the specific processes provided by a WPS implementation are defined by the owner of that implementation.

WPS makes it easy to create, publish, find, and bind to web services. It provides support for the competing REST and SOAP/WSDL approaches to web services, allowing the client to choose the method of discovery and invocation that suits their needs.

WPS defines three operations:

GetCapabilities returns service-level metadata
DescribeProcess returns an description of a "process" including its inputs and outputs
Execute returns the output of a "process"

WPS operations can be invoked using a standard web browser by submitting requests in the form of Uniform Resource Locators (URLs) via HTTP GET, or XML documents via HTTP POST. The content of such URLs or XML documents depends on which operation is requested. For example, when requesting an Execute operation the HTTP request identifies the inputs, the process to be executed, and the form of output to be provided.

WPS has the following properties

For a single output such as a GIF image, WPS can return the output directly
For multiple outputs, WPS returns the outputs embedded in an XML response document.
Inputs can be web-accessible URLs
Outputs can be stored as web-accessible URLs
Supports multiple input and output formats
Supports long-running processes

A WPS is usually not invoked directly. More often, it is invoked by a client application that provides the user with interactive controls. This client application may or may not be web-based.

WPS is still under development by the OGC. Public release of WPS version 1.0 is anticipated in mid-2007. Version 0.4.0 was released as an OGC Request for Public Comment and has been implemented by some early adopters.