1. An apparatus for processing a multidimensional string query, the apparatus comprising: an n-gram set generator configured to generate n-gram sets, for a multidimensional query of multi-attribute data; an n-gram set selector configured to select one or more n-gram sets from among the generated n-gram sets, based on posting list sizes, of a multidimensional n-gram index of multi-attribute data; a candidate set generator configured to generate a candidate set, by using posting lists corresponding to the selected n-gram sets; and a refinement processor configured to determine whether the multidimensional query is included in a document, based on the generated candidate set; wherein the multidimensional query comprises strings that are expressed in predetermined symbols, based on respective attributes; and wherein the predetermined symbols are designated to one or more respective sections, and wherein the one or more respective sections are obtained by dividing a range of an actual value of each of the attributes into the one or more respective sections.