A system to reduce a required memory area (storage capacity) and save time and effort for updating target attributes in aggregation processing is disclosed. The system for aggregating data includes an index storing unit for storing DtoK indices arranged in predetermined order, each of the indices specifying a list of attributes included in a target data item from identification information of the target data item, and a word list that is a list of attributes included in a plurality of the target data items, and an aggregation processing unit for finding, for each attribute, target data items including the attribute and executing aggregation processing for aggregating attributes whose relation with the target data items meets a predetermined standard. A link is created for each attribute in the word list for sequentially following an element in the index for each target data item, and target data items are found based thereon.