def uri_from_fields(prefix, *fields):
        """Construct a URI out of the fields, concatenating them after removing offensive characters.
        When all the fields are empty, return empty"""
        string = '_'.join(AlignmentHelper.alpha_numeric(f.strip().lower(), '') for f in fields)

        if len(string) == len(fields) - 1:
            return ''

        return prefix + string