Actually you're describing a classic 3-tier architecture (client<->application server<->database server), where the application server is in the network's DMZ, so that it can communicate with the client (via the internet) on the one hand, as well as the database server (which has no internet access) on the other.
There's actually no need to develop 2 separate applications for this, and it would be easier to implement using a single application, which during the development phase can be accessed via a regular (desktop or mobile) browser, and a native version created only when actually needed (i.e. just before moving to production, or if certain native capabilities such as camera access needs to be used). Creating the native version which seamlessly communicates with the application server is described in http://www.tersus.com/#Id=5585 (see the section with heading "Strategy 1 - Services modeled in the same application").
Note that in order to access Oracle from Tersus, you'll need to purchase a commercial license which provides access to commercial databases, see http://www.tersus.com/#Id=279 for more details.
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