Design Of Remote Heterogeneous Database Synchronous Based On Mail System

With traditional databases, computer networks and the rapid development of digital communication technology, the research and development of distributed database systems, which distributed data storage and processing are the main feature of, is attracts more and more attention. There are already lots of ways to achieve remote communication to system and database replication technology. Also, many kinds of large database systems integrate database replication technology. But because its development is more complicated and heterogeneous database systems can not achieve data replication technology, the development is to some extent restricted.In the shipping industry, the use of distributed database technology has become a trend. With this technology, database applications can be extended to the ship, replicate data to management authorities, and automate the transmission of information between ship and shore. However, because of the special circumstances of shipping, it's hard to keep the network between ships and land-based enterprises always connected, which bring difficulty to the database synchronization between ship and shore.To overcome the difficulty in the above scenario, this paper provides a realization of the technology of two-way data synchronization between distributed heterogeneous database systems in the ship and shore by using e-mail.With characteristics of ease of use, stable performance and low cost, e-mail technology undoubtedly plays an irreplaceable advantage to achieve remote data replication. However, the inherent characteristics of e-mail system also make it the existence of following weakness: can-be-fake, messy-display, sometimes-lose, and out-of-sequence. In this paper, end-to-end encryption technology and RSA digital signatures is used to solve e-mail forgery problem; encoding message with ASCII before sending out is employed to resolve the messy display problem; the mechanism of confirmation and retransmission when error/timeout is applied to solve the e-mail message loss and out-of-sequence issues.Considering the cost of sending message from ship, the message is smaller in size the better. Therefore, the database update information carried by e-mail should be compressed. We use LZW lossless compression algorithm to compress mail attachments for reducing the amount of data and cost.