Resilientt Dataa Replicationn Mechanismss Forr Battlee Commandd Systems 2 Associated Technologies and Issues 2.1 Active Databases and Triggers

As the move to automate the information distribution process progresses, commercial distributed database practices have become the focus of many system designs. However, at the lower echelons, where wireless communications are the rule, this has not been the case because (1) the problem is still viewed as a sophisticated, e–mail challenge to be solved using procedural messages rather than databases and (2) the rigidity of commercial practices does not support an environment that is characterized by the unfortunate combination of time–critical distribution requirements and tenuous communications. This paper describes the concepts and rationale behind resilient, as opposed to robust, data replication and introduces a ‘‘promiscuous’’ mechanism that addresses the requirement for highly selective information distribution when bandwidth is tenuous. The final conclusion is not surprising: ‘‘There is no free lunch.’’