Intro To RDBMS

This tutorial explains what a relational database management system (RDBMS) is.  It describes basic RDBMS functions and contrasts RDBMS with other database management systems (DBMS) and alternate forms of data storage.
Database design is also discussed, including the important concept of database normalization. The most widely used database management systems and RDBMS vendors are introduced at the end of the tutorial.
The integration of Internet applications with relational databases is explored in the "Dynamic Website" portion of our site.  It explains how an Internet website can be integrated with a RDBMS to create a dynamic, data driven website.

                          

A relational DBMS is special system software that is used to manage the organization, storage, access, security and integrity of data.  This specialized software allows application systems to focus on the user interface, data validation and screen navigation.  When there is a need to add, modify, delete or display data, the application system simply makes a "call" to the RDBMS.
Although there are many different types of database management systems, relational databases are by far the most common.  Other types include hierarchical databases and network databases.
Although database management systems have been around since the 1960s, relational databases didn't become popular until the 1980s when the power of the computer skyrocketed and it became feasible to store data is sets of related tables and provided real-time data access.
             

By storing data in a RDBMS, undesirable data redundancy can be avoided.  This not only makes data management easier, but it also makes for a flexible database that can respond to changing requirements.

 http://rdbms.ca/database/alternatives.html 

When designing a relational database, it is normally a good thing to "normalize" the database.  There are different degrees of normalization, but in general, relational databases should be normalized to the "third normal form".  Simply put, this means that the attributes in each table should "depend on the key, the whole key and nothing but the key".
An example of a de-normalized database table is provided below. The database designer has assumed that there will never be a need to have more than two order items in any one order:

By moving repeating groups of attributes to a separate database table, the database design becomes more flexible. A single order can now support any number of order items; not just just two. The primary key (PK) of the Order Item table is the "Order Nbr" (represented by the relationship) plus the "Order Item Nbr":

The "Order Item Description" field is dependent on the "Order Item Code"; not the unique identifier of the Order Item Table (i.e. "Order Nbr" + "Order Item Nbr").  By creating a classification table, the database become even more flexible.  New codes can easily be added.  The "Order Item Description" for a given code can easily be altered should the need ever arise (e.g. "blue widget" => "light blue widget"):

A RDBMS alone will not solve all data management issues. A good data analyst and/or database analyst is needed to design a flexible and efficient relational database.

                                          RDBMS VENDORS

There are many different vendors that currently produce relational database management systems (RDBMS).  Relational databases vary significantly in their capabilities and in costs.  Some products are proprietary while others are open source.  The leading vendors of RDBMS are listed below:

RDBMS Vendors	RDBMS
Computer Associates	INGRES
IBM	DB2
INFORMIX Software	INFORMIX
Oracle Corporation	Oracle
Microsoft Corporation	MS Access
Microsoft Corporation	SQL Server
MySQL AB	MySQL
NCR Teradata
PostgreSQL Dvlp Grp	PostgreSQL
Sybase	Sybase 11

 
                                        ALTERNATIVES TO RDBMS
Although most businesses manage their corporate data in relational database management systems (RDBMS), many businesses still operate application systems that use flat files for data storage.  Many of these systems are legacy "batch" systems that can't support online data transactions.  A flat file can be stored on computer tape or on a hard drive of some sort.
Network databases such as IDMS became popular in the 1980s, when computers were much less powerful than the ones that exist today.  Although network databases supported online transactions, the databases were relatively inflexible.  Once a database was designed, it was often costly to implement changes.
Hierarchical databases were also popular in the 1970s and 1980s.