Logical Database structures
Logical structures include tablespaces, schema objects, data blocks, extents and segments.
Database is logically divided into one or more tablespaces. Each tablespace creates one or more datafiles to physically store data.
Schema objects are the structure that represents database's data. Schema objects include structures such as tables, views, sequences, stored procedures, indexes, synonyms, clusters and database links.
Data block represents specific number of bytes of physical database space on disk.
An extent represents continuous data blocks that are used to store specific data information.
A segment is a set of extents allocated for a certain logical structure.
Physical database structure
The physical database structure comprises of datafiles, redo log files and control files
Datafiles contain database's data. The data of logical data structures such as tables and indexes is stored in datafiles of the database. One or more datafiles form a logical unit of database storage called a tablespace.
Redo log files
The purpose of these files is to record all changes made to data. These files protect database against failures.
Control files contain entries such as database name, name and location of datafiles and redo log files and time stamp of database creation