Oracle database is comprised of three types of files. One or more datafiles, two are more redo log files, and one or more control files.
There are tablespaces and database's schema objects.
A database is divided into Logical Storage Unit called tablespaces. A tablespace is used to grouped related logical structures together.
Every Oracle database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.
Each databases logically divided into one or more tablespaces one or more data files are explicitly created for each tablespace .