1. A system configured to associate base content with relevant content, the system comprising: a parsing module configured to parse the base content to form parsed base content; a unit-dictionary module including a plurality of query units; a unit-extraction module configured to extract query units included in the unit dictionary from the parsed base content, wherein the query units extracted from the base content are referred to as the extracted-query units; a unit-ranking module configured to rank the extracted-query units based on at least one of relevance scores and revenue-generation amounts for the query units; and a unit-matching module configured to generate at least one association between the base content and the relevant content based on whether the extracted-query units and at least one of query units and keywords associated with the relevant content are the same.