Given the Limitations:
Oracle Database data in geographical region X cannot be physically moved to region Y due to legal constraints
Oracle Database data in region X can only be accessed remotely from region Y

Given that the volume of data accessed across region with be medium i.e., the OLTP application Z at region Y will access Oracle data from region X remotely. There will be no OLTP application Z at region X where Oracle database data is located.

Questions:
1. What is the recommended (best practice) method of accessing region X Oracle data remotely from region Y using OLTP application Z?
2. What other options are available to remotely access region X Oracle data from region Y?
3. What are the pros & cons of using Oracle DB links to access region X Oracle data from region Y?
4. Is Oracle Gateway required for access of region X Oracle data from region Y given that end-to-end it is only Oracle database data?

Thanks in advance for your valuable inputs.