1、 外文原文 Distributed Database Development Centralized databases have been in large-scale use in the data processing industry since the early 1970s.Distributed databases are very much more sophisticated than centralized databases ,and they involve complex software to handle problems such as concurrency
2、control , deadlock prevention and the maintenance of data integrity during multi-site updates .It is only recently that these software problems have been understood ,and products which incorporate this software have only very recently started to appear on the market. The present generation of DDBs m
3、ainly involve replication of databases at several sites ,rather than distribution of individual databases. The next generation of DDBs , though ,is likely to involve distribution of data over several geographic nodes ,in order to place data as close as possible to the location at which the highest r
4、ate of activity takes place . With these databases it is likely that multi-site updates will be more commonly used than at present. This will involve very careful preparation of recovery procedures in order to ensure that the risk of loss of data integrity is driver down to an absolute minimum. In some installations it will also be necessary to carefully monitor both the network and the DDBs on an on-going basis, in order to enable the operations staff to react rapidly to any situation in which
