PREFIX dgp8:      <http://data-gov.tw.rpi.edu/vocab/p/8/>
SELECT DISTINCT ?date ?value ?g
WHERE{
graph ?g{
      ?o dgp8:site_id "" .
       { ?o dgp8:ozone_8hr_daily_max ?value .
        ?o dgp8:ddate ?date  } 
        UNION
       { ?o dgp8:rawhr ?value .
        ?o dgp8:date_time ?date } 
 }
}