FTAM — Why does File derive from PropertySetDef?

The spec states the File interface derives from
CosProperty::PropertySetDef and lists the properties that can be
associated with a file: is_directory, creator, size, mod_time,
create_time, access_rights, name, complete_file_name and num_children.

Under what circumstances could a client validly change the property
mode of one of these? A client could certainly change the values of
some of these but not the modes of the properties themselves.

Unless an example can be provided that shows a need to modify the
property mode, File should derive from PropertySet not PropertySetDef.

Change FileSystemEntry Interface to derive from PropertySet.