1. A computer-readable storage medium that contains therein a program causing a computer to execute a process comprising: collecting a plurality of tables from a storage; calculating, for each field of each of the plurality of tables, a field score which is a value based on the appearance frequency of each value in the field; selecting tables different from each other as a relation source table and a relation destination table from the plurality of tables, the relation source table having a field different from each of fields in the relation destination table, selecting a relation source field which is a field in the relation source table and a relation destination field which is a field in the relation destination table, and generating a combination of the relation source field and the relation destination field as a relation; and calculating, for each relation generated, a relation strength from the relation source field to the relation destination field based on the appearance frequency of each value in the relation destination field duplicated in each relation source field, the relation strength indicating correspondence between values in the relation source field and values in the relation destination field, and calculating a relation score which is a value based on the relation strength thus calculated, a field score of the relation source field, and a field score of the relation destination field.