The relational model presents an orderly, predictable and intuitive approach to organizing, manipulating and viewing data.
RDBMS Terminology:
Relational data consists of relations. A relation (or relational table) is a two dimensional table with special properties. A relational table consists of a set of named columns and an arbitrary number of rows. The columns are called as attributes and rows are called as tuples. Each attribute is associated with a domain. A domain is a set of values that may appear in one or more columns.
Properties of Relational Data Structures:
Relational tables have six properties, which must be satisfied for any table to be classified as relational. These are:
1) Entries of attributes are single valued: Entry in every row and column position in a table must be single valued. This means columns do not contain repeating groups.
2)Entries of attribute are of the same kind: Entries in a column must be of same kind. A column supposed to store salary of an employee should not store commission.
3)No two rows are identical: Each row should be unique. This uniqueness is ensured by the values in a specific set of columns called the primary key.
4) The order of attributes is unimportant: There is no significance attached to order in which columns are stored in the table. A user can retrieve columns in any order.
5) The order of rows is unimportant: There is no significance attached to the order in which rows are stored in the table. A user can retrieve rows in any order.
6) Every column can be uniquely identified: Each column is identified by its name and not its position. A column name should be unique in the table.
