Database Management System and SQL

Summary:

Database Management Systems (DBMS) are software designed to store and retrieve user data while maintaining security. They overcome problems in conventional file-processing systems like data redundancy and inconsistency, difficulty accessing data, and more. Within a DBMS, an Entity Relationship (ER) diagram graphically represents the logical structure of the database, defining entities, attributes, and relationships. There are different types of entities (strong, weak) and relationships (unary, binary, etc.), and cardinality constraints regulate these relationships. Attributes are the properties of an entity, and they can be simple, composite, multi-valued, derived, or key attributes. Constraints ensure data accuracy, defining rules like domain constraints, tuple uniqueness, and referential integrity. Keys, such as super key, candidate key, primary key, etc., uniquely identify tuples within a relation, and functional dependencies describe how some attributes determine others. The decomposition of relations can be lossless or lossy, affecting how sub-relations can be rejoined. Normalization makes the database consistent by reducing redundancies and ensuring data integrity through various Normal Forms (1NF, 2NF, 3NF, BCNF). Transactions are a vital aspect of DBMS, representing a logical unit of work and comprising operations like read and write, and their states, like active, partially committed, committed, or failed, control their execution flow.

Excerpt:

Database Management System and SQL

Database: A database is a collection of related data representing some aspect of the real world. A database system is designed to be built and populated with data for a certain task.

Database Management System (DBMS) is software for storing and retrieving users’ data while considering appropriate security measures. It consists of a group of programs which manipulate the database. The DBMS accepts the request for data from an application and instructs the operating system to provide the specific data. In large systems, a DBMS helps users and other third-party software to store and retrieve data.

Database management systems were developed to handle the following difficulties of typical File-processing systems supported by conventional operating systems.
1. Data redundancy and inconsistency
2. Difficulty in accessing data
3. Data isolation – multiple files and formats
4. Integrity problems
5. Atomicity of updates
6. Concurrent access by multiple users
7. Security problems