[Geoserver-devel] [JIRA] (GEOS-8229) provide distinct values in a WFS GetPropertyValue request

GeoServer GeoServer Developer
1

Iurie Maxim created an issue

GeoServer / New FeatureGEOS-8229

provide distinct values in a WFS GetPropertyValue request

Issue Type:

New FeatureNew Feature

Assignee:

Unassigned

Created:

20/Jul/17 10:52 PM

Priority:

MediumMedium

Reporter:

Iurie Maxim

In many INSPIRE data themes there are certain elements of feature types that can have tens , hundreds, or even thousand values from a codelist or enumeration. An example of such a codelist is the species names codelist from eu-nomen that contains more than 300,000 species names (i.e.: http://www.eu-nomen.eu/portal/taxon.php?GUID=urn:lsid:faunaeur.org:taxname:305289 is the codelist value for the wolf) or the pollutants that are monitored by Environmental Monitoring Facilities.

From the perspective of an user it is important to know which species/pollutants/distinct values are provided trough WFS, because based on these distinct values the user will filter the data (i.e.:by posting/using a stored query).

Currently there are two options:
1, The data provider creates an SQL layer (http://geoserver.geo-solutions.it/edu/en/adding_data/add_sqllayers.html) and provides details to the users in the WFS GetCapabilities document for users to know how to use the SQL layer and what the provided result means. This solution allow the data provider to provide the distinct values, but has as disadvantage that the user will most probably not aware that there is such a function and how to use it. The main disadvantage is that the user cant do nothing if the data provider will create is not creating such SQL layer and is not describing how to use it.
2. The user is performing a WFS GetPropertyValue request and get all the values of a certain element of a feature type. The main disadvantage is that the user is not able to retrieve only the distinct values of that element, so in some cases the list will be huge and the result not usable.

The proposed solution is to add an optional non-standard element to the GetPropertyValue, named “distinct”, that can have two values “true” or “false”.
If making a “GetPropertyValue” KVP or POST request with the attribute “distinct=true” the WFS should return only the distinct values of that element/property.

As this is an important function, that we saw on the internet that was required by several users, (but they wrongly indicated storedQuery as a solution) we think that this should/could be part of the next WFS standard release.

Such a function exist in REST from 2012.

This topic will be covered at the INSPIRE Conference during the Workshop on Practical INSPIRE Practices.

Waiting for any suggestion, reaction or action,
Iurie Maxim

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