Bitmap-tree indexing for set operations on free text

Here we report on our implementation of a hybrid-indexing scheme (bitmap-tree) that combines the advantages of bitmap indexing and file inversion. The results we obtained are compared to those of the compressed inverted file index. Both storage overhead and query processing efficiency are taken into consideration. The proposed new method is shown to excel in handling queries involving set operations. For general-purpose user queries, the bitmap-tree is shown to perform as good as the compressed inverted file index.