WPS DescribeProcess Operation
The DescribeProcess operation allows WPS clients to request a full description of one or more processes that can be executed by the service. This description includes the input and output parameters and formats and can be used to automatically build a user interface to capture the parameter values to be used to execute a process.
|Request||Required||Identifies service request. Must be "DescribeProcess".|
|Service||Required||Identifies service type. Must be "WPS".|
|Version||Required||Identifies service version. Defaults to the latest available version, currently 1.0.0.|
|Language||Optional||Determines the language of the human-readable content of the response. Consists of a valid 2 or 5 digit RFC 4646 language tag (e.g "en", or "en-CA") supported by the server as indicated in the Capabilities document.|
|Identifier||Mandatory||List of one or more process identifiers as listed in the Capabilities document, separated by commas, for which a description is requested. The use of the Identifier "ALL" is restricted as an option for an Identifier in the DescribeProcess operation. When "Identifier = ALL", the DescribeProcess operation shall return process descriptions for all processes served up by the WPS instance.|
HTTP GET method using KVP (mandatory)
All WPS servers shall implement HTTP GET transfer of the DescribeProcess request, using KVP encoding. The KVP encoding of the DescribeProcess request shall use the parameters specified above. An example of a DescribeProcess request via HTTP GET is:
HTTP POST method using XML (optional)
WPS servers may also implement HTTP POST transfer of the DescribeProcess request, using XML encoding only. The request parameters are encoded as XML elements, with their contents identical to those indicated in the parameter table shown above according to the DescribeProcess request XML schema. The following example indicates the contents and structure of a DescribeProcess request encoded in XML.
<DescribeProcess service="WPS" version="1.0.0" language="en">
SOAP-encoded DescribeProcess requests and responses use SOAP document-style encoding (also called message-style or document-literal encoding), as described in [OWS 06-094]. WPS SOAP messages simply contain a normal XML-encoded request or response wrapped in a SOAP envelope.
The normal response to a valid DescribeProcess operation request shall be a ProcessDescriptions data structure, which contains one or more Process Descriptions for the requested process identifiers. Each Process Description includes the brief information returned in the ProcessOfferings section of the service metadata (Capabilities) document, plus descriptions of the input and output parameters. Each process can have any number of input and output parameters.
Each parameter is described by a data structure that specifies the allowable formats, encodings, and units of measure (when applicable). For each input parameter, the process can indicate that it needs one of the following:
- "ComplexData" (such as XML or imagery), in one of the following allowable combinations of format (mimetype, encoding, and schema). The value of this complex data structure can be (either) directly encoded in the Execute operation request or made available through a web accessible URL.
- "LiteralData", with a specified data type, allowable values, default value, and allowable unit of measure indicated.
- "BoundingBoxData", using one of the supported coordinate reference systems. For each output parameter, the process can indicate similar information about the corresponding forms of output parameters. Again, there are three types of process outputs: ComplexOutput, LiteralOutput, and BoundingBoxOutput.
The DescribeProcess response is encoded in XML according to the DescribeProcess response XML schema.
- View schema documentation
- Download complete OGC schema package (note, WPS requires modification of an OWS Common file, as indicated in Annex B of the WPS specification).
When a WPS server encounters an error while performing a DescribeProcess operation, it shall return an exception report message as specified in Clause 8 of [OGC 06-121r3]. The allowed exception codes shall include those listed in Table 5 of Subclause 7.4.1 of [OGC 06-121r3].
For more information on structuring requests, please see the WPS Standard.