Information-Optimal Reflectionsof View Updates on Relational Database Schemata

摘要

For the problem of reflecting an update on a database view to the main schema, the constant-complement strategies are precisely those which avoid all update anomalies, and so define the gold standard for well-behaved solutions to the problem. However, the families of view updates which are supported under such strategies are limited, so it is sometimes necessary to go beyond them, albeit in a systematic fashion. In this work, an investigation of such extended strategies is initiated for relational schemata. The approach is to characterize the information content of a database instance, and then require that the optimal reflection of a view update to the main schema embody the least possible change of information. To illustrate the utility of the idea, sufficient conditions for the existence of optimal insertions in the context of families of extended embedded implicational dependencies (XEIDs) are established. It is furthermore established that all such optimal insertions are equivalent up to a renaming of the new constant symbols which were introduced in support of the insertion.