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; 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; a candidate set generator configured to generate a candidate set 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.