7.4.7. DescribeStoredQuery¶
The DescribeStoredQuery operation is used to provide the details of one or more stored queries offered by the server. The following listing exemplifies a DescribeStoredQuery request.
<?xml version="1.0" encoding="UTF-8"?>
<wfs:DescribeStoredQueries service="WFS" version="2.0.0"
xmlns:wfs="http://www.opengis.net/wfs/2.0">
<wfs:StoredQueryId>http://www.opengis.net/def/query/OGC-WFS/0/GetFeatureById</wfs:StoredQueryId>
</wfs:DescribeStoredQueries>
The <wfs:StoredQueryId> child element provides the unique identifier of
the stored query (see ListStoredQuery operation
in Section 7.4.6). By
providing more than on unique identifier through multiple
<wfs:StoredQueryId> elements, the descriptions of separate stored
queries can be requested in a single DescribeStoredQuery operation. If
the <wfs:StoredQueryId> element is omitted, a description of all stored
queries available at the WFS server is returned to the client.
The above request will produce a response similar to the following listing.
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<wfs:DescribeStoredQueriesResponse
xmlns:fes="http://www.opengis.net/fes/2.0"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:wfs="http://www.opengis.net/wfs/2.0">
<wfs:StoredQueryDescription id="http://www.opengis.net/def/query/OGC-WFS/0/GetFeatureById">
<wfs:Title xml:lang="en">Get feature by identifier</wfs:Title>
<wfs:Abstract xml:lang="en">Retrieves a feature by its gml:id.</wfs:Abstract>
<wfs:Parameter name="id" type="xs:string">
<wfs:Title xml:lang="en">Identifier</wfs:Title>
<wfs:Abstract xml:lang="en">The gml:id of the feature to be retrieved.</wfs:Abstract>
</wfs:Parameter>
<wfs:QueryExpressionText returnFeatureTypes=""
language="urn:ogc:def:queryLanguage:OGC-WFS::WFS_QueryExpression"
isPrivate="false">
<wfs:Query typeNames="schema-element(core:_CityObject)">
<fes:Filter>
<fes:ResourceId rid="${id}"/>
</fes:Filter>
</wfs:Query>
</wfs:QueryExpressionText>
</wfs:StoredQueryDescription>
</wfs:DescribeStoredQueriesResponse>
Every WFS implementation must at minimum offer the GetFeatureById stored query having the unique identifier http://www.opengis.net/def/query/OGC-WFS/0/GetFeatureById as shown above. This stored query takes a single parameter id of type xs:string and returns zero or exactly one feature whose resource identifier matches the id value. For the 3D City Database WFS, the id value is evaluated against the gml:id of each feature in the database to find a match.
The returnFeatureTypes attribute lists the feature types that may be
returned by a stored query. Note that this string is empty for the the
GetFeatureById query. Consequently, the query will return a feature
instance of all advertised feature types if its gml:id matches. The set
of advertised feature types can be influenced in the config.xml settings
file.
The DescribeStoredQuery operation allows the following XML attributes.
XML attribute
|
O / M
|
Default value
|
Description
|
service
|
M
|
WFS (fixed)
|
The service attribute indicates the
service type. The value “WFS” is fixed.
|
version
|
M
|
2.0.x
|
The version of the WFS Interface
Standard to be used in the
communication.
|
handle
|
O
|
The handle parameter allows a client to
associate a mnemonic name with the
request that will be used in exception
reports.
|
A KVP-encoded DescribeStoredQueries request is shown below.
http[s]://[host][:port]/[context_path]/wfs?
SERVICE=WFS&
VERSION=2.0.2&
REQUEST=DescribeStoredQueries&
STOREDQUERY_ID=http%3A%2F%2Fwww.opengis.net%2Fdef%2Fquery%2FOGC-WFS%2F0%2FGetFeatureById
The supported KVP parameters are listed in the following table.
KVP parameter
|
O / M
|
Default value
|
Description
|
SERVICE
|
M
|
WFS (fixed)
|
see above
|
VERSION
|
M
|
2.0.x
|
see above
|
STOREDQUERY_ID
|
O
|
A comma-separated list of stored query
identifiers to describe.
|