Preserving consistency in nested transactions

The support of advanced applications such as CAD/CAM (computer-aided design and manufacturing) by nonstandard database systems (NDBs) has become important in database system research. Because complex integrity constraints are important, NDBSs have to provide a flexible mechanism to deal with them. For this purpose, the nested transaction concept developed for advanced applications is combined with the concept of levels of consistency. Each level of a nested transaction hierarchy is associated with a specific type of consistency, which is guaranteed at this level. The implementation is based on the existence of a recording routing, called when consistency violations are found, and a checking routine, called at the end of a (sub)transaction, for each type of consistency. The approach allows for tailoring the actions of both routines to the specific needs imposed by a particular type of consistency. The overall flexibility and the extensibility of the approach are illustrated by its implementation in the PRIMA project