One of the fundamental problems that constantly arises in information retrieval is that the user does not know what he or she is looking for in the database. However, this is not the fault of the user.
Useful databases are usually large collections of fairly heterogeneous information.
Even the database maintainers may not know all the types of information contained in the database. Without knowing exactly what is contained in a database, it is impossible to formulate a query with enough detail to extract the proper documents from a database. Studies have shown that a query from a typical user consists of only a few keywords. For a large database, one or two keywords are not enough to help the query engine find the documents that are useful to the user. Even research librarians, who are specifically trained to formulate queries, have trouble developing useful queries.