Virtual schemas and bases
We have informally presented the functionality of a view mechanism for object-oriented databases. The approach is intended to favor the dynamic nature of intensional and extensional data by allowing it to be easily and intensively explored.
A virtual schema defines a context on which application programs can operate. Its activation, which results in the creation of a virtual base, represents a context switch and provides a means for dealing with the dynamics of database applications which is not favored by conventional object-oriented models.
There are yet several issues not yet fully resolved such as the placement of virtual classes in the hierarchy, strategies for solving resolution conflicts, or the lazy evaluation of virtual and imaginary extensions. Furthermore, it is necessary to explore how the view mechanism can be used in several contexts such as schema updates, object versionning, integrity constraint verification, and active databases. In particular, the use of deductive capabilities in conjunction with a view mechanism seems to be a promissing approach which remains to be studied.
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