Highly reliable online system

A database synchronization control system comprising an original computer center connected by a multiplexed circuit to a backup computer center and a terminal adapted for selective connection to said original computer center and said backup computer center, wherein:

• said original computer center includes:
• an original database;
• means for processing a transaction received from said terminal to update a record forming a first updated record in said original database;
• means for transmitting said first updated record via said multiplexed circuit;
• and,
• said backup computer center includes:
• a backup database;
• means for storing said first updated record transmitted from said original computer center via said circuit into said backup database, and processing said transaction received into said original computer center from said terminal to update a record in said backup database when the terminal is connected to said backup computer center.

A database synchronization control system comprising:

• a main computer center including a main database and a backup database;
• means for reflecting contents of said main database into said backup database using on-line communication;
• a backup computer center including a sub database;
• a plurality of terminals adapted for selective connection to said backup computer center;
• means for grouping, upon a failure of said means for reflecting, said plurality of terminals into a first group of terminals adapted for connection to said main computer center, and a second group of terminals adapted for connection to said backup computer center independently;
• and,
• means for integrating said main database and said sub database by reflecting update information of said sub database obtained by updating by said second group of terminals and update information of said main database obtained by updating by said first group of terminals, respectively, to said main database on a basis of the contents of said sub database, and to said sub database on a basis of the contents of said main database, for restoration of said main database and said sub database in response to said failure.