Before revision: The program neither knows nor cares how underlying files holding the data are organized, and, depending on whether an SQL interface module to handle differences between different database systems was used , might be completely unaware what database was being used.
After revision: The program neither knows nor cares how underlying files holding the data are organized, and, depending on whether an SQL interface module to handle differences between different database systems was employed(compatibility layer)system , might be completely unaware what database was being used.