Precise detection and proper handling of view maintenance anomalies in a multidatabase environment

A global view in a multidatabase system is defined as a query against base relations. When the global view is materialized, any update to the corresponding base relations needs to be propagated to the materialized view. This is known as view maintenance. Different maintenances of the same materialized global view for different local updates may interfere with each other. As a result, the view may be incorrectly maintained (view maintenance anomaly). In order to correct the problem, we often need to precisely detect the occurrence of each anomaly. In a distributed environment, the departure order of a set of messages from one site may be different from the arrival order of these messages at another site due to unpredictable network routings and delays. In such an environment, precise detection of the occurrence of each anomaly is a difficult problem. The authors propose a method for precisely detecting the occurrence of each maintenance anomaly for global views defined by SPJ queries. Their method takes into consideration the possibility that messages may be delivered and received in different orders across the network.