Each work process on an application server must have a
database interface if you want to make the R/3 system independent of the
database system, and also to use it correctly despite the differences in the
SQL syntax between various databases. By means of this interface only, the R/3
system can communicate with the database. All of the database requests from the
R/3 system are converted into the correct Standard SQL statements for the
database system by the database interface. In order to perform this function,
it has to use a database-specific component, which shields the differences
between database systems from the rest of the database interface. You have to
choose the appropriate layer when installing the R/3 system. A user can access
a database from a program through Open SQL and Native SQL.