2.2 DBMS functionalities

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From a functional perspective, the contributions expected from a DBMS are:

	Support the concepts defined in the data model. In order to represent data properties. This level of representation is not necessarily related to the internal representation in the form of files. It usually includes the definition of specific types and the definition of consistency rules.
	Make transparent data sharing between different users. This means that multiple users should be able to use the database concurrently and transparently.
	Ensure confidentiality of data. It is necessary to specify who has the right to access or modify all or part of a database. We must therefore guard against illegal tampering whether intentional or accidental. This requires firstly a user identification, the formation of user groups with potential recoveries and secondly, a specification of privilages (add, delete, update). It is clear that ensuring the confidentiality of data generates a time overhead in request handling.
	Ensure compliance with the consistency rules defined on the data. A priori, after each modification on the database, all rules of consistency must be checked on all data. Obviously, such an approach is impractical for performance reasons and must identify ways to find exactly what rules and what data are likely to be affected by manipulations performed on the database. These treatments must be performed without stopping the system.

2.2 DBMS functionalities

	Being resistant to failure. This is to protect data against hardware failure or software whether intentional or accidental.
	Possess a high storage capacity. Thus enabling data management up to several billion bytes. Storage capacities of computers are steadily rising. However, user needs are also growing stronger. With the rise of multimedia data (text, image, sound, video) needs are even greater. The storage units are moved from the megabyte (106) to gigabyte (109), then to terabyte (1012), peta-byte (1016), and we start talking about exabytes (1018) even zettabyte (1021).
	To answer queries with a level of acceptable performance. A query requires searching data in a database based on some conditions. that may involve conditions. Computer power is not the only possible answer to the problems of performance. Query optimization can be very effective to ensure good performance.