How do I fix this XML schema? - xsd

Question

I am trying to use JAXB on my XML schema with IntelliJ Ultimate. This is the schema from the IndoorGML website. However, the IDE says there is something wrong with it.
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.opengis.net/indoorgml/1.0/core"
xmlns:gml="http://www.opengis.net/gml/3.2" elementFormDefault="qualified" version="1.0.3">
<xs:annotation>
<xs:documentation>
IndoorGML is an OGC Standard. Copyright (c) 2014,2015,2016,2018 Open Geospatial Consortium. To obtain additional rights of use, visit http://www.opengeospatial.org/legal/.
</xs:documentation>
</xs:annotation>
<!--
======================================================================
-->
<xs:import namespace="http://www.opengis.net/gml/3.2" schemaLocation="http://schemas.opengis.net/gml/3.2.1/gml.xsd"/>
<!--
======================================================================
-->
<xs:element name="IndoorFeatures" type="IndoorFeaturesType" substitutionGroup="gml:AbstractFeature"/>
<!--
</xs:schema>
In the last line in substitutionGroup="gml:AbstractFeature", the IDE marks AbstractFeature in red with the message "Cannot resolve symbol 'gml:AbstractFeature'". Does anyone know why? (The XSD file has more tags before the closing schema tag which I didnt' put here because it's a couple hundred lines.)
Thanks in advance! :)

Answer 1

The reported error is on this reference: substitutionGroup="gml:AbstractFeature"
...which is attempting make 'IndoorFeatures' a member of a substitution group that is defined in another namespace.
But which namespace? The namespace identified by the prefix 'gml'. And which namespace is that? The answer is here: xmlns:gml="http://www.opengis.net/gml/3.2"
So we need to find out where that namespace is imported into this XSD. That is done here:
<xs:import namespace="http://www.opengis.net/gml/3.2" schemaLocation="http://schemas.opengis.net/gml/3.2.1/gml.xsd"/>
I think the reason for the error is fairly obvious now, but I will go ahead and complete the answer. The XSD which defines that namespace is identified here:
schemaLocation="http://schemas.opengis.net/gml/3.2.1/gml.xsd"
Clearly, your application cannot resolve that URL or is not allowed to access it.
How can you fix it?
If you can get a copy of the XSD then you can either
a) save it to a local folder and change the schemaLocation attribute to point to the local folder, or
b) Define a schema resolver that maps the URL to your folder location.
Not sure whether IntelliJ supports schema resolvers, but I expect it does.