resource, either the local collection, or a high-quality
external resource, is proposed for query expansion on a perquery basis. The two proposed query expansion approaches
are thoroughly evaluated using two standard Text Retrieval
Conference (TREC) Web collections and from the
experimental results, there is a statistically significant
improvement compared with the baselines. They concluded
that the adaptive query expansion mechanism is very
effective when the external collection used is much larger
than the local collection and it can improve the effectiveness
and robustness of query expansion.