Storage and processing technologies: databases
Basic concepts and definitions of the database
The basis of the information system is the collection, reliable storage, retrieval, data processing and updating.
Electronic files on physical media (in external memory), in which the data is structured in such a way that different users and programs can use them, are called databases (DB ).
Databases provide full-scale and high-quality work of the whole enterprise and its subdivisions, allowing to collect, systematize and represent in the necessary form the information necessary for making managerial decision.
The main requirements for DBMS are as follows:
1 . Consistency of data - the requirement integrity of the database - maintaining complete and consistent information.
The notion of transactions ("all or nothing") is associated with the data integrity requirement. So, when you make an order for a certain product, you need to perform the following operations: order registration and reservation of a certain quantity of goods, as well as reduction of the quantity of the given goods in the warehouse. If a failure occurs at any stage of the data change, then the integrity of the database will be violated. To prevent such violations, you enter a transaction Order ", in which you either need to perform all necessary operations on the database (the product is sold, its stock in stock is reduced) or return the database to the initial state (the goods are not sold, its quantity in the warehouse has not changed).
2. Relevance of the data. At any given time, the information contained in the database must be reliable.
3. Multidimensional data usage - is the process of getting information from various sources into a single database and the ability to use it from any department of the enterprise in accordance with access rights and functions.
4. The ability to modify the system - the ability to modify its data and complement it with new features without affecting the overall system.
5. Reliability (the integrity of the database should not be affected by technical failures of the equipment).
6. Speed of access - provide quick access to the required information, especially when many users work.
To meet all the requirements for databases, the database concept is formulated, which has two aspects:
1) the data structure must be independent of the programs that use this data;
2) all data management should be centrally managed by the database management system, effective access to data, interaction between the database and users of the system, between the database and application programs implementing certain data processing functions.
The main functions of the DBMS are:
• managing data in external and operative memory and providing effective access to them in the process of solving problems;
• maintaining data integrity and managing transactions;
• maintaining a system log of changes to the database to ensure the recovery of the database after a technical or software failure;
• implementation of support for the language of data description and query language;
• Ensure data security.
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