2. Features of a DBMS

The prime purpose of a relational database management system is to maintain data integrity. This means all the rules and relationships between data are consistent at all times.

But a good DBMS will have other features as well.

These include:

• A command language that allows you to create, delete and alter the database (data description language or DDL)
• A way of documenting all the internal structures that make up the database (data dictionary)
• A language to support the manipulation and processing of the data (data manipulation language)
• Support the ability to view the database from different viewpoints according to the requirements of the user
• Provide some level of security and access control to the data

The simplest RDBMS may be designed with a single user in mind e.g. the database is 'locked' until that person has finished with it. Such a RDBMS will only cost a few hundred pounds at most and will have only a basic capability.

On the other hand an enterprise level DBMS can support a huge number of simultaneous users with thousands of internal tables and complex 'roll back' capabilities should things go wrong.

Obviously this kind of system will cost thousands along with a need to have professional database administrators looking after it and database specialists to create complex queries for management and staff.