A data file is created when a 'create tablespace' or 'alter tablespace' command is executed. Creating a data file of size 10MB actually allocates 10MB space on the hard disk.

If a tablespace is declared to contain 100 data files one slot per data file is reserved in the control file.

There are four types of data files -- system data files application (or user) data files temporary data files (used by oracle to store temp data while executing complex SQL statements) and rollback data files.

It is possible to resize a datafile. The command which will serve this purpose is

A data file stores data in binary pattern. Even database stored physically in datafile.. we could not access datafile directly to access record.it is maintained ny operation system.

The data physically stored in the datafile. We can associate one or more datafile for a single tablespace but can not assign one datafile to multiple tablespaces. Datafiles only contains the committed data but sometimes uncommitted as well. we can increase the size of the datafile but can not shrink below the High Water Mark. Datafiles can be taken offline read only & begin backup stage.

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datafiles comes under the physical structure of the database.

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It is used to store the actual data.. each datafile can be associated with one tablespace only.. two datafiles cannot belong to different tablespace.. but two datafiles can belong to same tablespace.

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we cannot change the system datafiles assocaited with system tablespace.. but we can change the user datafiles associated with users tablespaces

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we can resize the datafile we can add new datafile to the same tablespace so whenever database runs lack of space either we can change the datafile size or we can add new datafile to the same tablespace..