Recognization of FeatureCollections in deegree

[dstenger]

Background

deegree GML tools CLI is used to generate configuration from an INSPIRE schema. However, the generated configuration is empty. We analyzed this and the result was that some FeatureTypes are recognized as FeatureCollections. There is no configuration written for FeatureCollections.
The problem occurred with INSPIRE schema Geophysics and FeatureTypes ge_gp:GeophProfile and ge_gp:Campaign.

What does the GML specification say?

The specification says: "A GML feature collection is any GML feature with a property element in its content model whose content model is derived by extension from gml:AbstractFeatureMemberType (see 9.9.2)"

How does deegree behave?

FeatureTypes are considered as FeatureCollection in method ​isGML32FeatureCollection() if they have a property which is either derived from "AbstractFeatureMemberType" or "FeaturePropertyType".
There is also following comment in the code:

// handle deprecated FeatureCollection types as well (their properties are not
// based on
// AbstractFeatureMemberType, but on FeaturePropertyType)

How is this use case (INSPIRE) handled by deegree?

The INSPIRE schema has properties which are derived from "gml:FeaturePropertyType" and, thus, those FeatureTypes are considered as FeatureCollections by deegree.
In this case, the property "sam:sampledFeature" defined by https://schemas.opengis.net/sampling/2.0/samplingFeature.xsd causes the problem as it is of type "gml:FeaturePropertyType":

...
<element name="sampledFeature" type="gml:FeaturePropertyType" maxOccurs="unbounded" nillable="true" block="#all">
...

Why is deegree behaving like this?

The "AbstractFeatureCollectionType" is defined in ​https://schemas.opengis.net/gml/3.2.1/deprecatedTypes.xsd and includes a sequence of elements of type "FeaturePropertyType" (element featureMember):

...
<element name="featureMember" type="gml:FeaturePropertyType">
  <annotation>
    <appinfo>deprecated</appinfo>
  </annotation>
</element>
...
<complexType name="AbstractFeatureCollectionType" abstract="true">
  <annotation>
    <appinfo>deprecated</appinfo>
  </annotation>
  <complexContent>
    <extension base="gml:AbstractFeatureType">
      <sequence>
        <element ref="gml:featureMember" minOccurs="0" maxOccurs="unbounded"/>
        <element ref="gml:featureMembers" minOccurs="0"/>
      </sequence>
    </extension>
  </complexContent>
</complexType>
<element name="AbstractFeatureCollection" type="gml:AbstractFeatureCollectionType" abstract="true" substitutionGroup="gml:AbstractFeature">
...

So, the deprecatedTypes schema gives a hint why deegree behaves like this.

What are possible solutions?

• Update method isGML32FeatureCollection(): Recognization of FeatureCollections basing on FeaturePropertyType for all types marked with 'deprecated'.
• Update method isGML32FeatureCollection(): Recognization of FeatureCollections basing on FeaturePropertyType only for types in GML namespace.
• Update method isGML32FeatureCollection(): Recognization of FeatureCollections basing on FeaturePropertyType not for types in INSPIRE namespace.
• Allow FeatureCollections when writing SQLFeatureStore configuration generally (configurable via parameter).

[stephanr]

At first glance, I can see that it will be difficult to implement a general solution in the core that comes without side effects.
And seeing the issue, I could assume that the insertion of data might also be affected (WFS-T and GMLLoader see [1]).
So, in theory, a possible solution may also include an extension point, where different type decisions can be inserted based on the used schema (URL).

References:

• [1]

  deegree3/deegree-tools/deegree-tools-gml/src/main/java/org/deegree/tools/featurestoresql/loader/GmlReader.java

  Lines 187 to 208 in f227d2c

  	boolean featureStreamFromFactory = false;
  	{
  	Iterator<FeatureStreamFactory> it = featureStreamFactories.iterator();
  	while (it.hasNext()) {
  	FeatureStreamFactory fac = it.next();
  	if (fac.isApplicableToDocumentRoot(xmlStream.getName())) {
  	featureStreamFromFactory = true;
  	this.featureStream = fac.createStream(xmlStream, gmlStreamReader);
  	}
  	}
  	}
  	if (featureStreamFromFactory) {
  	// loaded from external factory
  	}
  	else if (new QName(WFS_200_NS, "FeatureCollection").equals(xmlStream.getName())) {
  	LOG.debug("Features embedded in wfs20:FeatureCollection");
  	this.featureStream = new WfsFeatureInputStream(xmlStream, gmlStreamReader, WFS_20_MEMBER);
  	}
  	else if (new QName(WFS_NS, "FeatureCollection").equals(xmlStream.getName())) {
  	LOG.debug("Features embedded in wfs:FeatureCollection");
  	this.featureStream = new WfsFeatureInputStream(xmlStream, gmlStreamReader, GML_MEMBER, GML_MEMBERS);
  	}