Fundamentals of Extraction

Table:
Table is a structure consisting of set of rows and columns. The intersection of rows and columns is called a cell. The attribute in the table cell is called field. Every field maintains field name datatype length, decimal places, output length etc., This information is also called Meta Data. The sequence of the fields is called Header of table or structure of the table. Every field maintains field content or field value. The sequence of the field values is called record. The collection of records is called body. The combination of Header and Body is called Database table.
Every table definition in the ABAP Dictionary contains
Table fields: The field names and data type of the fields contained in the table are defined here( Data elements with data domains also maintain)
Foreign Key: Foreign Keys define the relationships between this table and other tables.
Technical settings- The technical settings defines how the table is created on the DB. It also includes data class(type of data) and size of the table.
Indexes: Indexes can be defined for the table to speed up data selection from the table to improve the reading performance.
Based on the Behaviour/Properties tables can be classified into 3 categories:
1.Transparent tables
2. Pooled tables
3. Cluster tables
Transparent tables are ABAP Dictionary tables that have a 1-1 relationship with DB tables stored in the underlying DB Management System.
Pooled Tables: It can be used to store control data example screen sequences program parameter or temporary data. Several pooled tables can be combined to form a "Table Pool'   corresponds to a physical table on the DB in which all the records of the allocated pool tables are stored.
Cluster tables contains contains text example: Documentation.Several cluster tables can be combined to form a table cluster. Several logical lines of different tables are combined to forma a physical record in the table type.
This permits object by object storage or object by object access. In order to combine tables in clusters atleast parts of the keys must be agree. Several cluster tables are stored in one corresponding table on the DB.