The paper analyses the factors that affect the IRS. These factors include the exact query formulation of user' s, the used keywords, correct selection of databases in an IRS and the evaluation/satisfact ion of the output by the user' s. The optimal search effectiveness of IRS with one- param-eter/two- parameter matching search and root- mean- square search is also explored. It points out that the above methods are an effective way to query formulation automatically for user' s.