How interface programming is done in apps

Can any one gives the detail information about how interface programming is done in apps?

Thanks in advance
Nagesh

Interface Program is written through SQL, PL/SQL.
PURPOSE: 1). Basic Integration
2). Imports valid data that is meaningful to Organization
3). Validate the integrity of any data Before introducing into oracle apps.
4). Imports data from legacy system.
5). Import data from one module to another.