How do every programming language and every scripting language?
Through a standard interface. For example if the application has been written using ODBC, then it just has to switch the drivers when the database changes. When someone develops a new database, the internals change, the implementation/approach might be different but they still want someone to use their database, don't they? In which case the implementors would add a standard interface? SQL? Now, if your application/scripts have been written to query the DB using SQL, you'd need very minor changes to switch between DBs. So, from the application side, one has to be cautious to write generic implementation (there can be some specifics which can be abstracted out with proper modular design) and from the database side there has to be standard interfaces.