gml:File

for efficiency reasons, GML also provides a means of encoding the range set in an arbitrary external encoding, such as a binary file.  This encoding may be "well-known" but this is not required. This mode uses the gml:File element.
The values of the coverage (attribute values in the range set) are transmitted in a external file that is referenced from the XML structure described by gml:FileType.  The external file is referenced by the gml:fileReference property that is an anyURI (the gml:fileName property has been deprecated).  This means that the external file may be located remotely from the referencing GML instance. 
The gml:compression property points to a definition of a compression algorithm through an anyURI.  This may be a retrievable, computable definition or simply a reference to an unambiguous name for the compression method.
The gml:mimeType property points to a definition of the file mime type.
The gml:fileStructure property is defined by a codelist. Note further that all values shall be enclosed in a single file. Multi-file structures for values are not supported in GML.
The semantics of the range set is described as above using the gml:rangeParameters property.
Note that if any compression algorithm is applied, the structure above applies only to the pre-compression or post-decompression structure of the file.
Note that the fields within a record match the gml:valueComponents of the gml:CompositeValue in document order.