Relevance Feedback [1, 2, 8] is a method not to use the
keywords in Query Expansion, but to expand query terms
and retrieve documents based on the relevance information
that users decide in the previously retrieved documents. The
retrieval system can retrieve new documents similar to the
corresponding documents that users decided to be relevant.
In addition, it can improve the retrieval effectiveness by
lowering the ranks of similar documents with non-relative
documents that are not relevant to the users’ prospective.