[Geoserver-users] app-schema and a mapping to generate xlink:href or xsi:nil on the same element

GeoServer GeoServer User
1

Geoserver users,

Below is a write-up of a problem I’ve encountered using app-schemas when specifying a mapping for an element whose attributes should be chosen dynamically. I’m also posting a solution that works for me. I would like to ask if anyone knows a simpler way to archive the same. Please let me know if I should include more information.

Kind Regards,
Lazar

Geoserver 2.4.4 App-Schema Mapping

Questions

  1. What is the simplest way to generate an element that should sometimes have an xlink:href attribute and sometimes have an xsi:nil attribute, where the choice is data-driven?
  2. As a last resort, is fiddling with geoserver’s private cache of XSD files an accepted technique for coercing it to produce required output?

Problem and workaround involving xlink:href and xsi:nil

Requirement

Generate

<gsmlga:eventProcess xsi:nil=“true” nilReason=“missing”>

or

<gsmlga:eventProcess xlink:href=“http://resource.geoscience.gov.au/classifier/ga/eventprocess/deposition” xlink:title=“deposition”>

Solution

App-schema mapping

gsml:relatedFeature/gsmlga:GeologicHistory/gsml:relatedFeature/gsmlga:GeologicEvent/gsmlga:eventProcess xlink:href if_then_else(isNull(EVENTPROCESS_URI), Expression.NIL, EVENTPROCESS_URI) xlink:title if_then_else(isNull(EVENTPROCESS_URI), Expression.NIL, EVENTPROCESS) gsml:relatedFeature/gsmlga:GeologicHistory/gsml:relatedFeature/gsmlga:GeologicEvent/gsmlga:eventProcess true xsi:nil if_then_else(isNull(EVENTPROCESS_URI), 'true', Expression.NIL) nilReason if_then_else(isNull(EVENTPROCESS_URI), 'missing', Expression.NIL)

Target element is gsmlgu:GeologicUnit. The schemas are

xmlns:gml=“http://www.opengis.net/gml/3.2”
xmlns:gsml=“http://xmlns.geosciml.org/GeoSciML-Core/3.2”
xmlns:gsmlga=“http://xmlns.geosciml.org/GeologicAge/3.2”

The above mapping works when EVENTPROCESS_URI is not null, but otherwise, it generates

<gsmlga:eventProcess xlink:href=“#null” xsi:nil=“true” nilReason=“missing”/>

In fact, even the following mapping

gsml:relatedFeature/gsmlga:GeologicHistory/gsml:relatedFeature/gsmlga:GeologicEvent/gsmlga:eventProcess

generates

<gsmlga:eventProcess xlink:href=“#null”/>

Since the above mapping is so minimal, I think that geoserver decides to insert the xlink:href attribute based on something it sees in the definition of eventProcess (where else?
it’s not the mapping and it’s not the data). Here is the definition from geologicAge.xsd

gsmlga:EventProcessTerm The eventProcess specifies the process or processes that occurred during the event. Examples include deposition, extrusion, intrusion, cooling.

Drilling further into the types, however, shows that xlink:href is not a required attribute.

When I change this definition, in my app-schema-cache, to




gml:targetElementgsmlga:EventProcessTerm</gml:targetElement>

The eventProcess specifies the process or processes that occurred during the event. Examples include deposition, extrusion, intrusion, cooling.

the mapping works as required. Now that eventProcess can be of any type, geoserver cannot infer that it should insert a null xlink:href attribute into the generated element. Why does it in the first place?

Note

The problem goes away if the requirements are changed to generate

<gsmlga:eventProcess xlink:href=“http://www.opengis.net/def/nil/OGC/0/missing” xlink:title=“missing”/>

or

<gsmlga:eventProcess xlink:href=“http://resource.geoscience.gov.au/classifier/ga/eventprocess/deposition” xlink:title=“deposition”>

and not use xsi:nil attribute at all. The mapping becomes straightforward.

gsml:relatedFeature/gsmlga:GeologicHistory/gsml:relatedFeature/gsmlga:GeologicEvent/gsmlga:eventProcess xlink:href EVENTPROCESS_URI xlink:title EVENTPROCESS

Kind Regards,
Lazar