LET $fp := //company[name = "Foobar Corporation"]/partners/partner :

FOR $ni IN //news_item
WHERE 
   EXISTS $t IN $ni//title : 
      (contains($t/text(), "Foobar Corporation")
       AND EXISTS $p IN $fp : contains($t/text(), $p/text())
      )
   OR EXISTS $par IN $ni//par :
      (contains($par/text(), "Foobar Corporation")
       AND EXISTS $p IN $fp : contains($par/text(), $p/text())
      )
RETURN
   <news_item>
      $ni/title,
      $ni/date
   </news_item>