In Fig. 5, all the keywords have the same frequency.
The B+
-tree and bloom filter perform a little better than
Merge-Join in most of the tests since these two algo-
rithms perform best when the frequencies of the key-
words vary greatly. While all the keyword lists in Fig.
5 have the same size, B+
-tree is a little better than
Merge-Join as the B+
-tree lookup is more efficient than
the Merge-Join scan. The bloom filter reduces the I/O
cost and is better than the other two methods.