“…They employ, R-tree 1,2,4,6,10 , spatial grid 5,7 , quadtree 3,8,11 , TMIS 9 , etc. to organize the spatial information of spatial objects and employ table-based structure [12][13][14][15][16] to maintain the textual keyword information to achieve top-k frequent spatial keyword queries. Since, in STDB, the textual keywords of spatial object are diverse and complex, the number of frequent features of them is often more than data itself, and the retrieval of frequent features by above table-based index structure still needs a high cost.…”