Connecting mobile devices directly to an RDBMS is not recommended. It is technically possible, but there are serious security implications, not to mention performance, battery life, etc.
This forum is for a product specifically designed to solve this problem the right way: Oracle Database Mobile Server (DMS).
With DMS, you simply develop a standard Android application using the built-in local database, SQLite. (you can also use Berkeley DB on Android for a complete Oracle solution, this is especially helpful for large data sets). You then bundle the sync client with your application, and DMS will take care of the rest, keeping you local database in sync with the Oracle RDBMS backend.
You will need to define the relationship between the mobile and backend databases beforehand, this is done using a tool called Mobile Database Workbench (MDW). You can read about that here:
and you can browse all the docs here:
download here to try it out:
As added benefits, you get the ability for the app to function in disconnected mode, and it offers some basic device mgmt capability.