1. A method of processing a database designed for handling data of such data type which includes a plurality of instances and which enables said instances to be definitely determined with subscripts, said method comprising the steps of: receiving a query containing a predicate or alternatively a function which includes a plurality of designations for column data of said data type and designation of conditions concerning said column data; acquiring a set of instances which can be definitely determined by a same subscript from the instances which constitute the column data of said data type, said column data being specified in said predicate or alternatively specified by said function; and evaluating individual instances of said instance set acquired from at least two column data of said data type in view of the conditions specified in said predicate or alternatively specified by said function.