Physical and logical structure of database

In Oracle, there are 2 types of structure: physical and logical structure.

1. Physical Structure: it is simply the physical data files that you can see in a file manager. You can find most of them in the directory where your database is resided. Few types of file:
   • Data File: extension is DBF, where the data is stored.
   • Control File: extension is CTL, where the database current state is stored
   • Parameter File: extension is ORA, parameter file of all kind of database process include listener. Usually store in directory where you install your DBMS.
   • Redo Log: extension is RDO, store the changes of your database transaction before commit is issued.
     
2. Logical Structure: it only stay in memory, where physically store in physical file. It only appear when the database service is started, and only can be view by using certain database tools. Few types of logical structure:
   1. Tablespace: where the tables or data are stored. 1 tablespace can map to 1 or more data files.
   2. Segment: Smaller unit in tablespace, which can further categorized into data segment, index segment, temporary segment and rollback segment.
   3. Extend: Smaller unit in Segment.
   4. Block: Smaller unit in Extend.