1. A processing system comprising: at least one processor; and a memory in communication with the at least one processor, the memory being configured to store a search engine module that is executable by the at least one processor, the search engine module having instructions, that when executed by the at least one processor, cause operations to be performed, comprising: accessing a query; identifying a plurality of other queries that is associated with the query, the plurality of other queries including a plurality of query terms; calculating a diversity index of the plurality of query terms, the diversity index being a measure of diversity between the plurality of query terms, the diversity relating to an unlikeness between the plurality of query terms; comparing the diversity index to a threshold value; and expanding the query with the plurality of query terms based on the comparison.