TJS DescribeData Operation

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TJS DescribeData Operation


The DescribeData operation returns an XML document that describes all of the attributes for any dataset identified in the request. The response includes descriptive information about each attribute available from the service instance, and information that uniquely identifies that attribute. This description can be used to automatically build a user interface to identify the attribute data that the user would like to obtain from the service.


DescribeData Request

Parameters

Name Presence Description
service Required Identifies service type. Must be "TJS".
request Required Identifies service request. Must be "DescribeData".
version Required Identifies service version. Defaults to the latest available version, currently 1.0
language Optional Determines the language of the human-readable content of the response. Value is a two or five character IETF RFC 4646 language identifier.
FrameworkURI Required The URI of the spatial framework, as indicated in the DescribeFrameworks response.
DatasetURI Required The URI of the attribute dataset, as indicated in the DescribeDatasets response.
Attributes Optional The names of the attributes for which descriptions are requested from the server. Value is one or more Columnset/Attributes/Column names as found in the DescribeData response, in comma-delimited format. Attribute names are normally unknown during an initial DescribeData request to the server, and therefore this parameter is normally absent from such a request. If this parameter is absent, the response shall include descriptions of all attributes available for the specified dataset.

Methods

HTTP GET method using KVP (mandatory)

All TJS servers shall implement HTTP GET transfer of the DescribeData request, using KVP encoding. The KVP encoding of the DescribeData request shall use the parameters specified above. An example of a DescribeData request via HTTP GET is:

http://foo.bar/foo?
   service=TJS&
   request=DescribeData&
   version=1.0&
   language=en&
   FrameworkURI=http://nrcan.gc.ca/Provinces/2001&
   DatasetURI=http://statcan.ca/2001Census

Note: URL encoding of KVP values in this example has been removed for clarity.


HTTP POST method using XML (optional)

TJS servers may also implement HTTP POST transfer of the DescribeData operation request, using XML encoding only. The request parameters are encoded as XML elements, with their contents equivalent to those indicated in the parameter table shown above, and encoded according to the DescribeData request XML schema. The following example indicates the contents and structure of a DescribeData operation request encoded in XML.

<DescribeData service="TJS" version="1.0" language="en">
  <FrameworkURI>http://nrcan.gc.ca/Provinces/2001</FrameworkURI>
  <DatasetURI>http://statcan.ca/2001Census</DatasetURI>
</DescribeData>



DescribeData Response

Schema

The normal response to a valid DescribeData operation request shall be a DataDescriptions data structure, which contains descriptions of one or more Datasets for which data is available on this service. This document is encoded in XML according to the DescribeData response XML schema.

Examples


Exceptions

When a TJS server encounters an error while performing a DescribeData 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 TJS Standard.