Database Management System (DBMS) is a 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
ER diagram or Entity Relationship diagram is a conceptual model that gives the graphical representation of the logical structure of the database. It shows all the constraints and relationships that exist among the different components. An ER diagram is mainly composed of the following three components: - Entity Sets - Attributes - Relationship Set Example: Roll_no is a primary key that can identify each entity uniquely. Thus, by using a student's roll number, a student can be identified uniquely.
An entity set is a set of the same type of entities. ● Strong Entity Set: - A strong entity set is an entity set that contains sufficient attributes to uniquely identify all its entities. - In other words, a primary key exists for a strong entity set. - Primary key of a strong entity set is represented by underlining it. ● Weak Entity Set: - A weak entity set is an entity set that does not contain sufficient attributes to uniquely identify its entities. - In other words, a primary key does not exist for a weak entity set. - However, it contains a partial key called a discriminator. - Discriminator can identify a group of entities from the entity set. - Discriminator is represented by underlining with a dashed line.