Explain the concept of nested transactions and their application in database management systems.

Nested transactions are a mechanism that allows running additional, internal transactions within a single outer transaction. If the inner transaction completes successfully, changes are committed locally, but the final confirmation occurs only when the outer transaction is successfully completed.

This is useful when a complex operation is broken down into several logical parts, each of which must be atomic. For example, in a banking system, you might first check the balance (inner transaction), then deduct funds, and only if all parts succeed, commit the changes.

In database management systems, support for nested transactions can be implemented through savepoints, which allow rolling back part of the changes without canceling the entire transaction.