Formal conformance to the INSPIRE requirements does not automatically imply full usability of a dataset in GIS clients or web applications. Selecting the correct encoding options can make a difference to fully exploit in a GIS environment the information contained in data geometries and semantics.
Here follow some helpful tips to get the best when you try to use your GML file in GIS environment
Use the "urn" encoding for Coordinate Reference System
INSPIRE Technical Guidelines propose "to use the http URIs provided by the Open Geospatial Consortium as coordinate reference system identifiers". Nevertheless, the use of "http://www.opengis.net/def/crs/EPSG/0/" can cause incorrect geolocation of the GML data in some GIS tools, such for example QGIS.
The use of the "urn:ogc:def:crs:EPSG::" encoding to address the Coordinate Reference System in the GML file avoids such an inconvenience.
The example in the screenshot below shows how QGIS displays two files referring to Italian Protected Sites which differ only in the CRS encoding.
Nested structures and xlinks
In some cases currently available GIS software is not able to handle the nested structures of the GML encoding and xlinks efficiently.
For example QGIS cannot display directly by means of "GetFeatureInfo" tool the "xlink" and the nested properties of GML file.
To have access to such info, you have to install the "GML Loader"and the "Complex GML Info"plugins.