Relational Data Model (DBMS)

 A Relational Database Management System (RDBMS) is a database management system that is based on the relational model as introduced by Dr. E.F Codd. It should satisfies Codd's 12 rules but in practice there is no DBMS that satisfies all these rules. 

RDBMS stores data in  the form of related tables. RDBMS are powerful because they require few assumptions about how data is related or how it will be extracted from the database. As a result, the same database can be viewed in many different ways. 

An important feature  of relational systems is that a single database can be spread across several tables.

Today, popular commercial for large database include oracle, microsoft SQL server. 

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Properties of Relational Tables

1. Values are atomic 
2. Column values are of the same kind.
3. Each row is unique 
4. Each column has a unique name.
5. The sequence of rows is insignificance.
6. The sequence of columns is insignificance 

• Values are Atomic -

This property implies that column in a relational table are not repeating group or arrays. hence composite and multi-valued attributes are not allowed .

• Column Values Are Of The Same Kind 

In relational terms this means that all values in a column come from the same domain. for example, ename column contains only name of the employee. it never contains other information such as address and DOB etc.

• Each Row Is Unique -

This property ensures that no two rows in a relational table are identical 

• The Sequence Of Columns Is Insignificant -

This property states that the ordering of the column in the column in the relational table has no meaning columns can be retrived in any order and in various sequence.

• The Sequence Of Row Is Insignificant -

This Property is analogous of the one above but applies to rows instead of columns .

• Each Column Has A Unique Name -

This property states that the column name of each column should be unique.

                        DBMS and RDBMS

• In DBMS relational between two tables or files are maintained programmatically.

• DBMS does not support client/server architecture

• DBMS does not support distributed database.

• In DBMS there is not tight security of data.

• Each table is given an extension in DBMS.

• DBMS may satisfy less than 7 to 8 rules of Dr.E.F.Codd.

                                   RDBMS

• In RDBMS, relationship between two tables or files can be specified at the time of table creation.

• Most of the RDBMS supports elient server architecture.

• Most of the RDBMS supports Distributed database.

• In RDBMS there are multiple levels of security .

                 (a) Logging in at O/S level
                 (b) Command level
                  (c) object level 

• Many tables are grouped in one database in RDBMS.

• RDBMS usually satisfy more than 7 to 8 rules of Dr.E.F.Codd.