The　authors　provide　a　method　based　on　an　index　and　realize　keyword　search　in　the　free　form　over　relational　databases.　Using　the　saved　knowledge,　the　authors　create　an　index　and　improve　the　classic　ranking　strategy　in　Information　Retrieval　by　assigning　different　weight　values　to　attributes.　Then　the　top-N　answers　are　returned　for　a　keyword　query.　Experimental　results　for　a　large　real　dataset　indicate　that　the　performance　of　the　method　is　efficient　and　effective.