Data Mode:

If the called form and the calling form share the similar set of libraries by default, a form runtime tool loads multiple copies of the library file like one copy for each form. Therefore, the memory resources of the system are not efficiently used. If similar set of libraries are attached to the called form and the calling form, the Data Mode argument could be set to SHARE_LIBRARY_DATA. This ensures in which only one copy of the PL/SQL library is loaded and used through both the forms. The system resources are therefore efficiently used.

If various set of libraries are attached the forms then the Data Mode argument can be set to NO_SHARE_LIBRARY_DATA.