Query expansion

Query expansion (QE) is the process of reformulating a given query to improve retrieval performance in information retrieval operations, particularly in the context of query understanding. In the context of search engines, query expansion involves evaluating a user's input (what words were typed into the search query area, and sometimes other types of data) and expanding the search query to match additional documents. Query expansion involves techniques such as: Finding synonyms of words, and searching for the synonyms as well Finding semantically related words (e.g. antonyms, meronyms, hyponyms, hypernyms) Finding all the various morphological forms of words by stemming each word in the search query Fixing spelling errors and automatically searching for the corrected form or suggesting it in the results Re-weighting the terms in the original query Query expansion is a methodology studied in the field of computer science, particularly within the realm of natural language processing and information retrieval. Search engines invoke query expansion to increase the quality of user search results. It is assumed that users do not always formulate search queries using the best terms. Best in this case may be because the database does not contain the user entered terms. By stemming a user-entered term, more documents are matched, as the alternate word forms for a user entered term are matched as well, increasing the total recall. This comes at the expense of reducing the precision. By expanding a search query to search for the synonyms of a user entered term, the recall is also increased at the expense of precision. This is due to the nature of the equation of how precision is calculated, in that a larger recall implicitly causes a decrease in precision, given that factors of recall are part of the denominator. It is also inferred that a larger recall negatively impacts overall search result quality, given that many users do not want more results to comb through, regardless of the precision.