Oracle Database gateways provide the ability to transparently access data in non-Oracle databases from an Oracle environment. You can create synonyms for the objects in a non-Oracle database and refer to them without having to specify a physical location. This transparency eliminates the need for application developers to customize their applications to access data from different non-Oracle systems, thus decreasing development efforts and increasing the mobility of the application.
Instead of requiring applications to interoperate with non-Oracle systems using their native interfaces (which can result in intensive application-side processing), applications can be built upon a consistent Oracle interface for both Oracle and non-Oracle systems.