/**
 * call-seq:
 *  webservice_url() -> string or nil
 * 
 * Return an URL for retrieving CD information from MusicBrainz' web service
 *
 * The URL provides the CD information in XML. 
 * See http://musicbrainz.org/development/mmd for details.
 *
 * Returns +nil+ if no ID was yet read.
 */
static VALUE mb_discid_webservice_url(VALUE self)
{
        if (rb_iv_get(self, "@read") == Qfalse)
                return Qnil;
        else
        {
                DiscId *disc;
                Data_Get_Struct(self, DiscId, disc);
                
                return rb_str_new2(discid_get_webservice_url(disc));
        }
}