A variant master table includes respective columns for variant ID, variant pattern, and pattern code. A composite primary key constraint for the variant master table is set by the columns for variant ID and pattern code. The respective processors reads variant information, verifies whether or not variant patterns for variant positions have been entered into the table, and for unentered variant patterns, attempts to insert a row of information into the table that includes the unentered variant pattern, a corresponding variant ID, and a pattern code allocated based on the variant master table. In cases in which the row of information violates a composite primary key constrain, the respective processor reattempts to insert an updated row of information in which the pattern code has been changed. The processors encode the variant information based on information entered into the variant master table.