File System vs DBMS — Advantages of a DBMS

To appreciate why a DBMS is used, it helps to see the problems of the older file-based (traditional file) system, in which each application program kept its own separate data files.

Problems of the file-based system:

• Data redundancy (duplication): the same data is stored in many files. A customer's name and address might appear in the sales file, the billing file and the delivery file. This wastes storage space and effort.
• Data inconsistency: because the same data is duplicated, an update made in one file but not the others leaves different files disagreeing with each other. If a customer changes address and only the sales file is updated, the billing file now holds the wrong address.
• Difficulty in accessing data: getting a new kind of report often needs a new program to be written, because the files are tied tightly to specific programs.
• Weak security: it is hard to control who can see or change which parts of the data when it is spread across many ordinary files.
• Poor data sharing and integrity: it is difficult for different departments to share the same up-to-date data, and there is no central mechanism to enforce validity rules.

A DBMS is designed to overcome exactly these problems. Advantages of a DBMS over the file system:

• Controlled redundancy: data is stored centrally, so duplication is minimised — each fact is ideally stored in one place.
• Consistency: because data is not needlessly duplicated, and updates happen in one central place, the data stays consistent.
• Data sharing: many users and applications can use the same central database at the same time.
• Data security: access can be controlled precisely through user accounts, passwords and permissions.
• Data integrity: validity rules (constraints) are enforced centrally so that only correct data is stored.
• Easy access and reporting: using a query language such as SQL, users can ask for exactly the information they need without writing a full program. …